THE  J.  PAUL  GETTY  MUSEUM  LIBRARY 


fj  Hl/ 


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THE 


CABINET  CYCLOPAEDIA. 

CONDUCTED  BY  THE 

REV.  DIONYSIUS  LARDNER,  LL.  D.  F.  R.  S.  L.  &  E. 

M  R.  I.  A.  F.  R.  A.S.  F.L.S.  F.  Z.S.  Hon.  F.  C.  P.  S.  &c.  &c. 

ASSISTED  BY 

EMINENT  LITERARY  AND  SCIENTIFIC  MEN. 

USEFUL  ARTS. 


A 

TREATISE 

ON  THE 

ORIGIN,  PROGRESSIVE  IMPROVEMENT,  AND  PRESENT  STATE 

OF 

THE  MANUFACTURE 

OF 

PORCELAIN  AND  GLASS. 


Cons  . 

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V'  %  >7 

.  '  LIZ 

33fjUa&cIi)I)ia:  '  j 

CAREY,  LEA,  &  BLANCHARD. 


1834. 


“  The  arts  may  be  said  to  imitate  nature,  or  to  help,  or  to  overcome 
and  advance  nature :  nor  are  they  therefore  to  be  esteemed  less  noble 
because  more  practicable,  since  our  best  and  most  divine  knowledge 
is  intended  for  action ;  and  those  may  justly  be  counted  barren  studies 
which  do  not  conduce  to  practice  as  their  proper  end.” 

Bishop  Wilkins. 


ti 


THE  J  PAUL  GETTV  CENTER 
LBmPY 


A 

TREATISE 

ON  THE 

ORIGIN,  PROGRESSIVE  IMPROVEMENT, 


AND 


PRESENT  STATE 

OF  THE 

MANUFACTURE 


OF 

PORCELAIN  AND  GLASS. 


PiitlattelpWa : 

CAREY,  LEA,  &  BLANCHARD. 


1834. 


LIST  OF  WOOD  ENGRAVINGS. 


PORCELAIN. 

.  Page 

1.  Throwing . . 

2.  Biscuit  Kiln  French  Improvement . •  .  58 

3.  Do.  do.  ib. 

4.  Do.  do.  59 

5.  Making  Tobacco  Pipes,  Roll . 87 

6.  Do.  do.  Needle . ib. 

7.  Do.  do.  Mould . ib. 

8.  Do.  do.  Kiln .  .  .  • . 88 


GLASS. 

1.  Double  Furnace .  .  128 

2.  Glass  Pot  or  Crucible . 130 

3.  Gathering  Rod . 137 

4.  Blowing . ib. 

5.  Pontil . 138 

6.  Transferring  from  Gathering  Rod  to  Pontil . ib. 

7.  Procello . 139 

8.  Fashioning . ib. 

9.  Annealing  Oven,  front  view . 142 

1 0.  Blowing  Crown  Glass . 146 

11.  Circular  Plate . 147 

12.  Casting  Plate  Glass . 160 

13.  Blowing  do.  Gathering . 167 

14.  Do.  do.  Cylinder . ib. 

15.  Do.  do.  Punching . 168 

16.  Do.  do.  Opening . ib. 

17.  Do.  do.  do . ib. 

18.  Do.  do.  Cutting . .  ib. 

19.  Do.  do.  Transferring  ...  ....  169 

20.  Do.  do.  Opening . ib. 

21.  Do.  do.  Cutting  .  . . ib. 

22.  Do.  do.  Spreading . 170 

23.  Thermometer  Tubes,  Drawing . 176 

A  2 


CONTENTS. 


PART  I. 

PORCELAIN  MANUFACTURE. 

CHAPTER  I. 

HISTORICAL  NOTICES  OF  THE  RISE  AND  PROGRESS  OF  POTTERIES 
AND  THE  PORCELAIN  MANUFACTURE. 

Probable  Origin  of  the  Art. — Ancient  Brick-making. — Roman  Bricks. — 
The  Potter’s  Wheel,  an  Implement  of  high  Antiquity. — Indian  Earth¬ 
enware. — Roman  Water-pipes. — Introduced  into  Britain. — Remains 
of  Ancient  Pottery  in  the  Kingdom. — Roman  Potteries  in  Stafford¬ 
shire. — Earthenware  made  in  an  Island  formerly  existing  near  Mar¬ 
gate. — Antiquity  of  the  Art  in  the  East. — Porcelain  first  brought  to 
Rome. — Figures  found  with  Egyptian  Mummies. — China  Wares 
brought  by  Portuguese  Traders. — Erroneous  Notions  concerning  their 
Composition. — Corrected  by  Pere  d’Entrecolles. — Discovery  by  De 
Botticher  in  Saxony. — Manufacture  attempted  in  France. — Investiga¬ 
tions  of  Reaumur. — Proper  Materials  discovered  in  France. — Jonas 
Hanway’s  Account  of  Collection  at  Dresden. — Works  established  at 
Berlin. — English  Potteries. — Dr.  Plot’s  Account. — Improvements  in 
Glazing. — White  Stoneware. — Advantages  of  Mr.  Wedgwood’s  Im¬ 
provements. — Largo  Exportations  by  Mr.  Wedgwood. — His  principal 
Inventions. — Characteristics  of  true  Porcelain. — First  made  by  Mr. 
Cookworthy  in  England. — Importance  of  the  Manufacture. — Porce¬ 
lain  of  Derby. — Of  Coalport. — Of  Worcester. — Of  Rotherham. — Duty 
on  Stoneware. — Its  Unproductiveness  and  Impolicy . Page  17 

CHAP.  II. 

GENERAL  DESCRIPTION  OF  INGREDIENTS  USED  IN  THE 
MANUFACTURE. 

Different  Branches  of  the  Art. — Ingredients  used. — Properties  of  Alu¬ 
mina. — Its  Infusibility. — Contraction  when  exposed  to  Heat. — Wedg¬ 
wood’s  Pyrometer. — Composition  of  Gems. — Great  Abundance  of 
Clay. — Properties  of  Silica. — Its  great  Abundance. — Sea  Sand. — In¬ 
capable  of  artificial  Solution  in  Water. — Dissolved  naturally. — Springs 
at  Carlsbad. — Boiling  Fountain  in  Iceland. — Fusion  of  Silex. — Kinds 
of  Clay  used  in  Potteries. — Their  various  Merits. — China  Clay  of 
Cornwall. — Mode  of  its  Preparation. — Its  Analysis. — Cornish  Fel¬ 
spar. — Its  Fusibility. — Steatite. — Earth  of  Baudissero. — Its  Analysis. 
— Cornish  Sopestone. — Spuma  Maris. — Its  Employment  in  Porcelain 
Works  in  Spain . 33 


Vlll 


CONTENTS. 


CHAP.  III. 

ON  THE  PREPARATION  OF  MATERIALS. 

Dilution  of  Clay. — Chemical  Examination  of  Water  necessary. — Rain 
Water. — Carefulness  of  German  Manufacturers. — Blunging. — Ma¬ 
chinery. - Preparing  Flints. - Burning. — Baking. — Grinding. — Dry 

grinding. — Brindley’s  improved  Mill. — Chert. — Care  required  in  se¬ 
lecting  Grinding  Stones. — Dilution  of  Flint  Powder. — Affinity  of 
Alumina  for  Silica. — Slip. —  Slip-kiln. — Method  of  evaporating  super¬ 
fluous  Moisture  — Working  the  Paste. — Time  necessary  for  temper¬ 
ing  it. — Proportions  wherein  Clay  and  Flint  are  united. — Difficulty 
of  ascertaining  this. — Slapping. — French  Manufactures. — Proportions 
of  Ingredients  used  by  them. — Ivao-lin. — Flint. — Gypsum. — Broken 
Porcelain. — Calcined  Bones. — Tender  Porcelain. — Its  Composition. 
— Porcelain  Earth  used  in  Berlin. — French  Potters  buy  their  Ma¬ 
terials  ready  mixed. — Advantages  of  this  Plan. — Ineligible  in  Eng¬ 
land. . 40 


CHAP.  IV 

ON  THE  FORMATION  OF  UTENSILS. 

Throwing. — Potter’s  Lathe. — Thrower. — Mode  of  Proceeding. — Pro¬ 
files. — Slurry. — Gauges. — Turning  Lathe. — Turning  and  Smoothing. 
— Moulding  Dishes,  &c. — Tools. — Steam  Machinery. — Engine  Lathe. 
— Milled  Edges. — Handler. — Formation  of  Handles,  Spouts,  &c. — 
Pressing. — Small  Ornamental  Figures. — Mode  of  affixing  them. — 
Method  of  making  Moulds. — Boiled  Plaster. — Great  Use  of  Gypsum 
in  making  Moulds. — Stoves. — Modelling. — Qualifications  requisite 
for  a  Modeller. — Increasing  Skill  of  Artists. — Fostered  by  Wedg¬ 
wood. — Mould-maker. — Method  of  his  working. — Casting. — Careful¬ 
ness  required  in  Drying . . 48 


CHAP.  V. 

ON  THE  PROCESSES  OF  FIRING  AND  GLAZING. 

Seggars. — Proper  Materials  for  these  wanting  in  England. — Not  so  in 
France. — Nungarrow  Work. — Why  discontinued. — Great  Estimation 
of  its  Wares. — Cause  of  Superiority. — Use  of  Seggars. — Their  Forms. 
— Mode  of  using  them. — Sevres  Manufactory. — Improved  Furnace. 
— Its  Advantages. — Description. — Chinese  Method  of  Firing. — Con¬ 
struction  of  their  Kilns. — Care  required  in  Baking. — Duration  of  Pro¬ 
cess. — Oven-man. — Trial  Pieces. — Annealing. — Biscuit. — Wine-cool¬ 
ers. — Glazing. — Composition  of  Raw  Glazes. — Bad  Effects  of  some  of 
these. — To  the  Public. — To  the  Workman. — Pernicious  Use  of  Ardent 
Spirits. — Glazes  invented  by  M.  Chaptal. — By  Mr.  Rose. — Porcelain 
Glazes. — French  Glazes. — Pallissy. — His  Experiments  in  Enamel- 


CONTENTS. 


IX 


ling. — His  Perseverance  and  Sufferings. — His  Success,  and  continued 
Firmness  under  Persecution. — Inferior  Glazes. — Low-priced  Wares. 
— Gloss  Oven. — Regulation  of  Temperature. — Qualities  that  deter¬ 
mine  the  Excellence  of  Porcelain. — Stone  Ware. — Its  Composition. — 
Lambeth  Potteries. — Modes  of  Glazing . 55 

CHAP.  VI. 

ON  THE  ART  OF  APPLYING  COLORS  AND  ENGRAVINGS  TO 
EARTHENWARE. 

Antiquity  of  Enamel  Coloring. — Specimens  from  Ancient  Egypt. — 
From  the  Royal  Works  at  Sevres. — Painted  Ware  of  Worcester. — 
Of  Staffordshire. — Of  Derby. — Of  Yorkshire. — Great  Services  of  Mr. 
Wedgwood  in  this  Branch  of  the  Manufacture. — Mystery  observed 
in  the  Preparation  of  Colors. — Publication  of  Processes  by  M.  Brong- 
niart. — Metallic  Oxides. — Addition  of  fluxing  Bodies  necessary — And 
why. — Colors  employed  for  tender  and  hard  Porcelain. — Vehicle 
used  with  the  Color. — Mode  of  their  Combination. — Description  of 
Colors. — Purple  and  Violet. — Red — Yellow — Blue — Green — Brown 
— Black — White. — Compound  Colors. — Precautions  necessary  in 
forming  those  Compounds. — Gilding. — Lustre  Ware. — Preparation  of 
Colors. — Enamelling  Kilns. — Trial  Pieces. — Method  of  Gilding  and 
Burnishing. — Copper-plate  Engravings. — Mode  of  transferring  Im¬ 
pressions  to  Earthenwares. — How  performed  in  France . 68 

CHAP.  VII. 

ON  THE  MANUFACTURE  OF  TOBACCO  PIPES. 

This  Manufacture  prosecuted  to  a  great  Extent. — Description  of  Ma¬ 
terial. — Rolling. — Boring. — Moulding. — Polishing. — Baking. — De¬ 
scription  of  Kiln. — Of  Crucibles. — Manufacture  in  Holland. — Origin¬ 
ally  conveyed  there  from  England . . . 86 

CHAP.  VIII. 

ON  THE  PORCELAIN  MANUFACTURE  OF  CHINA. 

Obscurity  wherein  its  Origin  is  shrouded. — Chiefly  practised  at  King- 
te-ching. — Supposed  Superiority  of  old  China  Ware. — Materials  em¬ 
ployed. — Koa-lin. — Pe-tun-tse. — Their  Preparation. — Oils  or  Varnish¬ 
es. — Their  Composition. — Hao-che. — Its  Superiority  to  Kao-lin. — 
Analysis  of  Kao-lin. — Extent  of  Factories  at  King-te-ching. — Great 
Number  of  Workmen  employed. — Preparation  of  Materials. — Method 
of  fashioning  Utensils. — Moulds. — Division  of  Labor. — Deficiency  of 
Chinese  in  the  Art  of  Design. — Their  excellent  Colors. — Numerous 
Hands  employed  in  decorating  each  Piece. — Bad  Effect  of  this  Sys¬ 
tem. — Blue  long  the  only  Color  used  for  painting  China  Ware. — 


CONTENTS. 

Mode  of  preparing  various  Colors. — Chinese  ignorant  of  Chemical 
Science.— Umiam.— Tsou-Tchi.— Kia-tsing.— Method  of  forming  it. 
—Chinese  Furnaces.— Passion  for  old  Porcelain.— Ku-tong.— Mock 
Antiques. — Reasons  for  Costliness  of  China  Ware  in  Europe.— High 
Prices  formerly  paid  in  China.— Finest  Specimens  not  brought  to 
Europe. — Porcelain  Tower  at  Nan-King. — Chinese  Potters  prepare 
Materials  for  the  Use  of  their  Descendants.-Common  Wares  made 
in  China.— Attempt  of  the  Emperor  to  transfer  the  Manufacture  to 
Pekin.— His  want  of  Success . 90 


PART  II. 

GLASS  MANUFACTURE. 

CHAPTER  I. 

ON  THE  NATURE  AND  PROPERTIES  OF  GLASS. - THE  HISTORY  OF 

ITS  INVENTION,  AND  MANUFACTURE. 

Nature  of  Glass. — Its  various  Properties. — Its  Utility  to  all  Classes. 
The  Assistance  it  lends  to  Science. — Admiration  of  the  Ancients— 
Excessive  Prices  formerly  paid. — Origin  of  its  English  Name.  Aris¬ 
totle’s  Problems. — First  invention  ascribed  to  the  Phoenicians. — Glass 
known  to  the  Ancient  Egyptians. — Manufactories  of  Alexandria— 
Utensils  found  in  Herculaneum.— Urns  in  British  Museum.— Mal¬ 
leable  Glass.— Taxon  Glass,  by  Alexander  Severus.— Portland  Vase 
—Glass  employed  in  forming  Windows.— Not  much  used  in  Eng¬ 
land  till  the  Eleventh  Century.— Privileges  granted  to  Manufactur 
ers  in  France.— Plate  Glass  casting.— Establishment  at  St.  Gobain.- 
Its  early  Failure— And  Revival.— Manufacture  commenced  in  Eng 
land.— Of  Flint  Glass.— Of  Plate  Glass.— Establishment  of  Britisl 
Cast  Plate  Glass  Company.— Chinese  unacquainted  with  Glass-mak 
ing.— Importance  of  the  Manufacture  in  England.— Glass  made  i 
Source  of  Revenue.— Bad  Effect  upon  Consumption.— Increase  of 

DiRy. _ Consequent  Decrease  of  Manufacture. — Diminution  of  Dub 

on  Plate  Glass.— Increase  of  Quantity  made . 10; 

CHAP.  II. 

ON  THE  VARIOUS  INGREDIENTS  EMPLOYED  IN  MAKING  GLASS 

Glass  always  composed  of  Silex  with  Alkali. — Different  Description 
of  Glass.— Sea  Sand— Soda  and  Potash— Pearlash.— Barilla- -Kelj 

-Wood-ashes— Nitre— Litharge— Minium— Manganese— Arser 

jc. — Borax. — Chalk . H 


CONTENTS. 


XI 


CHAP.  III. 

ON  THE  CONSTRUCTION  OF  FURNACES,  ETC. 

Stability  of  Furnace  essential. — Fritting  Furnace,  or  Calcar. — Its  Use. 
— Working  Furnace. — Double  Furnace. — Proportionate  Dimensions 
of  Furnace  and  Pots. — Wood  Furnaces. — Comparative  Consumption 
of  Fuel  in  Wood  and  Coal  Furnaces. — Annealing  Oven. — LierPans. 
— Glass  Pots. — Their  Formation  and  Seasoning . 125 

CHAP  IV. 

ON  THE  MANUFACTURE  OF  FLINT  GLASS. 

The  most  beautiful  and  costly  Kind  of  Glass. — Importance  of  its  Qual¬ 
ity  for  Optical  Purposes. — Experiments  for  its  Improvement. — Under¬ 
taken  by  the  Royal  Society. — Promoted  by  Government. — Distin¬ 
guishing  Properties  of  Flint  Glass. — To  what  owing. — Different  Com¬ 
positions. — Process  of  Melting. — Glass-gall. — Its  Use. — Curious  Phe¬ 
nomenon. — Implements. — Collecting  Glass  on  Rod. — Marver. — Parai- 
son. — Blowing. — Reheating. — Elongating. — Pontil. — Fashioning. — 
Detaching. — Removal  to  Annealing  Oven. — Moulding. — Annealing. 

•  — Why  indispensable. — Bologna  Phials. — Rupert’s  Drops . 131 

CHAP.  V. 

ON  THE  MANUFACTURE  OF  CROWN  GLASS,  BROAD  GLASS,  AND 
BOTTLE  GLASS. 

Description  of  Crown  Glass. — Harder  than  Flint  Glass. — More  difficult 
to  fashion. — Its  Composition. — In  France. — In  England. — Fritting. — 
Cullet. — Refining. — Sulphate  of  Soda. — Vegetable  Charcoal. — Gath¬ 
ering — Biowing — Reheating — Flattening. — Transferring  to  Pontil. — 
Twirling. — Expanding. — Opening. — Annealing. — Nice  Regulation  of 
Temperature  required  in  this  Process. — Qualities  of  Crown  Glass. — 
German  Glass. — Broad  Glass. — Inferior  to  Crown  Glass. — Its  Compo¬ 
sition. — Preparation. — Working. — Bursting. — Opening. — Annealing. 
— Bottle  Glass. — Manufacture  checked  by  Increase  of  Duty. — Com¬ 
position. — Restrictions  as  to  Materials. — Their  bad  Tendency. — Supe¬ 
riority  of  Bottle  Glass  for  certain  Purposes. — Materials  employed  in 
France. — At  Newcastle. — Fashioning. — Moulding. — Experiments 
suggested  by  Count  Chaptal. — Klingstein. — Volcanic  Granite . 143 

CHAP.  VI. 

ON  THE  MANUFACTURE  OF  PLATE  GLASS. 

Different  Descriptions  of  Plate  Glass. — Blown  Plates  limited  in  Size. — 
Cast  Plate  Works  at  Ravenhead. — Difficulties  of  the  Process. — Ma¬ 
terials. — Various  Compositions. — Borax. — Mixing  Materials. — Frit- 


Xll 


CONTENTS. 


ting. — Furnaces  and  Crucibles  at  St.  Gobain. — Potts. — Cuvettes. — 
Regulation  of  Firing. — Casting  Tables. — Arrangements  of  Foundery 
at  Ravenhead. — Annealing  Ovens. — Process  of  Casting  Plates. — 
Annealing. — Squaring. — Grinding. — Economical  Improvement. — 
Smoothing. — Emery  Powder. — Comparative  Value  of  large  and  small 
Plates. — Polishing. — Silvering. — Preparation  of  Amalgam. — Mode 
of  its  Application. — Blowing  Plate  Glass. — Punching. — Partial  Cut¬ 
ting. — Transfer  to  Pontil. — Completion  of  Cutting. — Opening. — An¬ 
nealing. — Sizes  of  Plates. — Effect  of  Sun’s  Rays  in  discoloring  Plate 
Glass . 154 

CHAP.  VII. 

ON  THE  COMPOSITION  OF  ARTIFICIAL  GEMS. 

Great  Interest  formerly  attached  to  this  Subject. — Different  Composi¬ 
tions  for  artificial  Gems. — Mode  of  Preparation. — Rock  Crystal  for¬ 
merly  employed. — Not  superior  to  Sand. — Diamond  Pastes. — Selec¬ 
tion  of  various  Pastes  for  imitating  different  Gems. — Reasons  for 
such  Selection . 171 


CHAP.  VIII. 

ON  THE  MANUFACTURE  OF  GLASS  FROM  CALCINED  BONES. 

Preparation  of  Bones. — Their  Vitrification. — Process  known  to  Becher. 
— Concealed  by  him. — Curious  Suggestion  as  to  its  Employment. — 
This  Glass  highly  electric  when  newly  made . 175 


CHAP.  IX. 

ON  THE  USE  MADE  OF  THE  BLOWPIPE,  AND  ON  VARIOUS  SMALL 
MANUFACTURES  OF  GLASS. 

Thermometer  Tubes. — Manner  of  giving  to  them  an  elliptical  Bore. — 
Blowpipe  and  Apparatus  described. — Materials  used. — Method  of 
working. — Sealing  Tubes. — Bending  and  Joining  Tubes. — Bulbs. — 
Spun  Glass. — Watch  Glasses. — Lunette  Glasses. — Glass  Beads. — 
Manufactory  at  Murano. — Striped  Tubes. — Mode  of  forming  Beads. 
— Sorting  them. — Numerous  Kinds  of  Beads. — Mock  Pearls. — Man¬ 
ner  of  their  Invention — And  Formation. — Dial  Plates. — How  form¬ 
ed. — Lettering  and  Figuring . 176 

CHAP.  X. 

ON  THE  FORMATION  OF  LENSES. 

Preparation  of  the  necessary  Tools. — Choice  of  Glass. — Grinding. — Pol¬ 
ishing. — Curdled  Lenses. — Means  used  for  avoiding  this  Defect. . .  189 


CONTENTS. 


Xlll 


CHAP.  XI. 

ON  THE  PRINCIPAL  DEFECTS  OBSERVABLE  IN  GLASS. 

StricE. — Render  Glass  unfit  for  Optical  Purposes. — Threads. — Render 
Glass  fragile. — Cause  of  this. — Tears. — One  of  the  greatest  Defects. 
— Render  Glass  useless. — Knots. — Bubbles. — Whence  they  proceed. 
— Do  not  much  affect  the  Quality  of  Glass. — Objects  to  be  attained 
for  avoiding  these  Defects. — M.  Guinand. — His  humble  Origin. — En¬ 
ergy  of  Character. — Examines  Telescopes  and  constructs  others. — 
Unable  to  procure  Glass  of  good  Quality. — Is  incited  to  examine  into 
the  Causes  of  Inferiority. — His  extraordinary  Perseverance  amidst 
Accidents  and  Difficulties. — His  ultimate  Success. — Accident  lead¬ 
ing  to  further  Improvement. — Prosecutes  his  Art  in  Bavaria. — Re¬ 
turns  to  Switzerland,  and  further  pursues  his  favorite  Object. — Dies. 
— Frauenhofer. — Rises  from  Obscurity  by  his  Talents. — His  Scientific 
Acquirements. — Produces  Specimens  of  perfect  Glass. — Dies  at  an 
early  Age. — Respect  paid  to  his  Memory . 192 

CHAP.  XII. 

ON  THE  SPECIFIC  GRAVITY  OF  GLASS. 

Importance  of  this  Quality. — Experiments  of  Loysel. — His  Reasoning 
and  Formulae. — Specific  Weight  augmented  by  Lime. — Mixed  Glass¬ 
es. — Their  specific  Weight. — Method  of  determining  this. — Influ¬ 
ence  of  Temperature  on  the  specific  Weight  of  Glass . 202 

CHAPTER  XIII. 

ON  THE  ART  OF  COLORING  GLASS. 

Antiquity  of  this  Art. — Specimens  of  Roman  Mosaic. — Analysis  of  these 
by  Klaproth. — Metallic  Oxides. — Gold  Purple. — Its  great  coloring 
Power. — Kunckel. — His  Proficiency  in  coloring  Glass. — Yellow  Col¬ 
or. — From  Silver. — From  Lead. — From  Tartar. — From  Beech  Wood 
Charcoal. — From  Oxide  of  Iron. — Green. — Black  Glass. — Blue. — Di¬ 
rections  found  in  old  Authors. — Imitation  of  the  Garnet. — Of  the 
Amethyst. — Of  the  Emerald. — Of  Sapphires. — Opaque  Glasses. — 
Black. — White. — Opal. — Ancient  Pictures  formed  of  colored  Glass. — 
How  executed. — Description  of  Ancient  Mosaics. — Most  recent  Pro¬ 
secution  of  this  Art. — Accidental  coloring  of  Plate  Glass  at  St.  Go- 
bain. — Ineffectual  Attempts  to  reproduce  this  Effect . .208 

CHAP.  XIV. 

ON  THE  ART  OF  STAINING  AND  PAINTING  GLASS. 

This  Art  more  recent  than  that  of  coloring. — Encouraged  by  the  Monks. 
— Early  Specimen  at  St.  Denis. — Art  never  much  cultivated  in  Eng- 

•  B 


XIV 


CONTENTS. 


land. — Splendid  Paintings  at  Gouda. — Directions  given  by  old  Au¬ 
thors  for  composing  Colors. — Fluxes. — Vehicles  for  diluting  Colors. — 
Description  of  various  Stains. — Method  of  floating  these. — Of  Paint¬ 
ing  on  Glass. — Imitation  of  Ground  Glass  with  transparent  Patterns. 
— Description  of  Kiln  employed. — Method  of  Firing. — Second  and 
third  Firing. — Ancient  Method  of  fixing  different-colored  Glasses  on 
each  other . 223 


CHAP.  XV. 

ON  THE  ART  OF  CUTTING,  ENGRAVING,  AND  ETCHING  ON  GLASS. 

Origin  of  the  Art  of  cutting  Glass. — Implements. — Manner  of  their  Em¬ 
ployment. — Frosting. — Patterns  produced  by  Moulding. — Engraving 
on  Glass. — Executed  with  the  Diamond. — Etching. — Schwanhard. — 
Difference  of  his  Practice  from  that  now  used. — Method  of  Etching. 
— Fluoric  Acid. — Glass  Incrustations. — Origin  of  the  Art. — Improve¬ 
ments  therein . _ . 235 


CHAP.  XVI. 

ON  THE  DEVITRIFICATION  OF  GLASS. 

First  observed  by  Neumann. — Experiments  of  Reaumur. — Substance 
known  as  Reaumur’s  Porcelain. — Inappropriateness  of  this  Name. — 
Uses  to  which  the  Substance  may  be  applied. — Common  Bottle  Glass 
most  proper  for  this  Conversion. — Method  of  effecting  the  Change. — 
Produced  solely  by  Heat. — Experiment  of  Dr.  Lewis. — Revitrifica¬ 
tion. — Experiments  of  Sir  James  Hall. — Proposal  suggested  thereby. 
— Observations  of  Guyton-Morveau. — Artificial  Intaglios. — Mock 
Onyxes. — Power  of  devitrified  Glass  to  bear  sudden  Changes  of  Tem¬ 
perature. — Experiments  with  colored  Glass. — Glass  devitrified  by 
burning  Lava. — The  Process  promoted  by  multiplying  the  Ingredi¬ 
ents  of  Glass. — Devitrified  Glass  conducts  Heat  more  perfectly  than 
when  vitreous. — Becomes  a  Conductor  of  Electricity. — Retains  this 
Property  when  revitrified . 243 


MANUFACTURE 

OF 


PORCELAIN. 


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A 


TREATISE 

ON  THE 

PROGRESSIVE  IMPROVEMENT  AND  PRESENT  STATE 

OF  THE 

MANUFACTURE 


OF 

PORCELAIN. 


CHAPTER  I. 

HISTORICAL  NOTICES  OF  THE  MANUFACTURE. 

Origin  of  the  Art. — Brickmaking. — Potter’s  Wheel.— Indian  Earthenwares. 
— Roman  Water-Pipes. — Remains  of  Ancient  Pottery. — Roman  Potteries 
in  Staffordshire. — Antiquity  of  the  Art  in  the  East. — Porcelain  first 
brought  to  Rome. — Figures  found  with  Egyptian  Mummies. — China- 
Wares  brought  by  Portuguese  Traders.— Discovery  by  De  Botticher  in 
Saxony. — Manufacture  attempted  in  France. — Investigations  of  Reau¬ 
mur. — Jonas  Hanway’s  Account  of  Collection  at  Dresden. — Works  at 
Berlin. — English  Potteries. — Plot’s  Account. — Improvements  in  Glazing. 
— White  Stone-Ware. — Wedgwood’s  Improvements. — Exportations  by 
Wedgwood. — His  Inventions. — Characteristics  of  True  Porcelain. — Porce¬ 
lain  of  Derby. — Of  Coalport. — Of  Worcester. — Of  Rotherham. 

The  formation  of  earthen  vessels  capable  of  containing  fluid 
substances  is  an  art  of  the  very  highest  antiquity.  In  the 
rudest  stages  of  society,  the  want  of  such  vessels  would  call 
forth  the  inventive  powers  of  mankind  ;  and,  probably,  the 
hard  shells  of  some  vegetable  productions,  such  as  gourds  and 
the  larger  descriptions  of  nuts,  would  be  first  adapted  to  the 
purpose.  The  pliant  and  infrangible  nature  of  the  skins  of 
animals  taken  in  the  chase  would,  at  a  very  early  period,  point 
them  out  as  convenient  recipients  for  fluids  ;  but  the  prepara¬ 
tion  of  these,  as  well  as  the  fashioning  and  hollowing  of 
wooden  bowls,  supposes  a  previous  knowledge  of  some  manual 
arts,  and  implies  the  possession  of  tools.  After  even  these 
had  been  attained,  and  supposing  that  the  existence  of  fire, 
and  its  use  in  preparing  food,  had  become  known,  vessels 
formed  of  wood,  or  of  the  hides  of  animals,  would  be  of  little 
use  in  rendering  that  knowledge  available.  Some  savage 
tribes  thus  circumstanced,  have,  indeed,  made  wooden  bowls 
subservient  to  this  purpose,  by  throwing  into  the  fluids  which 

B  2 


18 


PORCELAIN  MANUFACTURE. 


CHAP.  I. 


they  contain,  stones  previously  heated  in  the  fire.  This  man¬ 
ner  of  boiling  water,  and  of  cooking  provisions,  is,  however,  at 
best,  hut  an  inconvenient  process,  and  would  be  immediately 
abandoned  upon  the  discovery  that  certain  earthern  substances 
were  endowed  sufficiently  with  the  quality  of  resisting  the 
action  of  fire. 

It  must  continue  matter  of  doubt,  whether  the  fashioning 
and  hardening  of  clay  was  practised  first  by  the  brickmaker  or 
by  the  potter.  We  know  that  bricks,  thoroughly  burned, 
were  used  at  the  building  of  the  tower  of  Babel,  2200  years 
before  the  commencement  of  the  Christian  era,  and  600  years 
prior  to  the  carrying  away  into  captivity  of  the  Israelites. 
That  the  use  of  bricks,  for  the  purposes  of  building,  must  have 
become  exceedingly  common  at  this  last-mentioned  period,  is 
evident,  from  the  great  numbers  of  the  captive  Jews  who  were 
compelled  by  their  Egyptian  task-masters  to  prosecute  the 
manufacture.  It  appears  that  the  bricks  then  made  were  not 
artificially  burned ;  the  chopped  straw  which  entered  into 
their  composition,  and  which  served  to  hold  the  mass  together, 
would,  in  such  case,  have  been  destroyed.  Specimens  of  very 
ancient  Egyptian  bricks,  which  have  been  brought  to  this 
country,  confirm  the  supposition  that  the  heat  of  the  sun  was 
alone  employed  in  baking  them. 

Many  centuries  later,  the  Romans  conducted  the  manufac¬ 
ture  of  bricks  with  a  great  degree  of  perfection.  A  compari¬ 
son  of  very  ancient  Roman  ruins,  with  buildings  of  modern 
elevation,  will  show  at  once  how  superior  are  the  bricks  em¬ 
ployed  in  the  former,  both  as  regards  solidity  and  beauty. 
Specimens  of  the  potter’s  art,  if  even  any  such  existed  at  an 
equally  early  period,  could  not  be  expected  to  continue  in  be¬ 
ing  for  so  many  ages  ;  if,  indeed,  they  had  withstood  the  de¬ 
stroying  hand  of  time,  and  descended  to  the  present  day,  they 
would  not  bring  with  them  any  direct  testimony  of  their  date 
of  production,  and  could  throw  little  or  no  light  upon  the  ques¬ 
tion  of  priority.  It  is  certain,  however,  that,  in  very  remote 
ages,  the  potter’s  art  had  attained  to  a  considerable  degree  of 
usefulness,  since  the  earliest  authentic  records  allude  to  the 
potter’s  wheel  as  to  an  implement  of  then  high  antiquity. 

The  same  wants  would  arise  in  different  portions  of  the 
globe  ;  and  in  all  cases,  where  similar  means  for  their  grati¬ 
fication  presented  themselves,  it  is  not  surprising  that  these 
means  should  be  equally  embraced  by  all.  Accordingly,  it 
has  been  found,  in  newly-discovered  countries,  and  among 
people  comparatively  rude  and  unacquainted  with  most  of  the 
arts  which  conduce  to  human  convenience,  that  the  use  of 
earthen  vessels  has  been  enjoyed  for  ages  before  the  existence 


CHAP.  I.  HISTORICAL  NOTICES.  19 

of  the  people  was  even  surmised.  Among  other  proofs  of 
this  fact,  it  may  he  mentioned,  that  vases  have  been  found 
among  the  aboriginal  Indians  on  the  Mosquito  shore,  which, 
even  by  those  people,  were  preserved  as  memorials  of  antiquity. 
There  is  no  reason  to  doubt  that  these  vessels  were  the  man¬ 
ufacture  of  the  country  in  which  they  were  found,  as  the  re¬ 
mains  of  ancient  potteries  have  been  discovered  at  a  considera¬ 
ble  distance  up  the  Black  River  on  that  coast. 

There  would  be  little  advantage  in  entering  upon  an  in¬ 
vestigation  to  determine  the  precise  degree  of  antiquity  of  the 
potter’s  art,  if  even  there  existed  any  sufficient  guides  to  direct 
us  in  the  inquiry.  It  will  be  more  profitable  at  once  to  fore¬ 
go  all  fanciful  speculations,  and  to  commence  the  relation  of 
a  few  facts,  and  such  only  as  bear  the  stamp  of  authenticity. 
The  detail  of  these  need  not  occupy  much  time  or  space, 
which  may  be  more  advantageously  devoted  to  descriptions  of 
the  art  as  it  exists  in  the  present  day,  than  to  the  building  up 
of  theories,  the  truth  of  which  can  never  be  demonstrated. 

We  learn,  on  the  authority  of  Vitruvius,  who  wrote  in  the 
•Augustan  age,  that  the  Romans  then  made  their  water-pipes 
of  potter’s  clay.  This  people,  who  introduced  a  knowledge  of 
the  useful  arts  practised  by  themselves  wherever  their  con¬ 
quests  were  extended,  established  potteries  in  England,  where, 
among  other  articles,  similar  water-pipes  were  made.  Some 
of  these,  about  a  century  ago,  were  dug  up  in  Hyde  Park. 
They  were  found  to  be  two  inches  in  thickness,  and  were 
firmly  jointed  together  with  common  mortar  mixed  with  oil. 

It  has  been  asserted  that  the  ancient  Britons  were  in  the 
practice  of  making  pottery  before  the  invasion  of  this  country 
by  the  Romans ;  and  in  support  of  this  belief  is  brought  the 
fact,  that  urns  of  earthenware  have  been  taken  from  barrows 
in  different  parts  of  the  kingdom.  On  the  other  hand,  the 
concurring  testimony  of  various  writers  gives  reason  for  sup¬ 
posing  that  our  ancestors  were  in  those  days  supplied  with 
such  articles  by  the  Venetians.  Vestiges  of  considerable  Ro¬ 
man  potteries  are  discernible  in  many  parts  of  the  island,  and 
particularly  in  Staffordshire,  on  the  site  of  the  great  potteries 
which  have  so  long  been  carried  on  in  that  county.  In  sink¬ 
ing  pits  for  various  purposes,  remains  of  Roman  potteries  have 
occasionally  been  discovered  there  at  a  considerable  depth 
below  the  surface. 

Governor  Pownall  relates,  that  in  his  time  (1778)  the  men 
employed  in  fishing  at  the  back  of  the  Margate  Sands,  in  the 
Queen’s  Channel,  frequently  drew  up  in  their  nets  some 
coarse  and  rudely -formed  earthen  vessels,  and  that  it  was 
common  to  find  such  pans  in  the  cottages  of  these  fishermen. 


20 


PORCELAIN  MANUFACTURE. 


CHAP.  I. 


It  was  for  some  time  believed,  that  a  Roman  trading  vessel, 
freighted  with  pottery,  had  been  wrecked  here ;  but  on  more 
particularly  examining  the  spot,  called  by  the  fishermen  Pud¬ 
ding-pan  Sand,  some  Roman  bricks  were  also  discovered,  ce¬ 
mented  together,  so  as  to  prove  that  they  had  formed  part  of 
some  building.  Further  researches  showed  that,  in  Ptolemy’s 
second  book  of  Geography,  an  island  was  designated  as  existing 
in  the  immediate  vicinity.  Such  pans  as  were  recovered  in  a 
sound  state  were  of  coarse  materials  and  rude  workmanship — 
many  having  very  neatly  impressed  upon  them  the  name  of  At- 
tilianus ;  but  fragments  of  a  finer  and  more  fragile  description 
of  pottery  were  likewise  brought  to  the  surface ;  and  little  doubt 
remains  that,  during  the  time  of  the  Roman  ascendency  in 
England,  a  pottery  was  established  here  upon  an  island  which 
has  long  since  disappeared,  and  that  the  person  whose  name 
has  been  thus  singularly  preserved  was  engaged  in  its  man¬ 
agement. 

The  high  antiquity  of  the  art  in  China,  and  the  proficiency 
which  had  been  acquired  in  its  pursuit,  several  centuries  be¬ 
fore  the  produce  of  their  manufactories  found  its  way  to  Eu¬ 
rope,  will  be  shown  in  a  future  chapter.  Porcelain  of  superior 
quality  was  likewise  made  in  Japan  at  an  equally  early  period ; 
and  we  learn  from  Propertius,  that  at  a  very  remote  date,  the 
art  was  commonly  practised  in  Persia,  the  vessels  manufac¬ 
tured  there  joining  to  all  the  excellencies  possessed  by  the 
porcelain  of  China,  the  quality  of  resisting  the  action  of  fire 
to  a  degree  which  fitted  them  for  being  used  in  the  prepara¬ 
tion  of  food. 

Most  authors  who  have  noticed  in  any  way  the  state  of 
commerce  among  the  ancients,  have  referred  to  the  Vasa 
Murrhina  particularly  described  by  Pliny,*  and  mentioned  by 
various  Greek  and  Roman  authors.  The  general  opinion  was 
long  in  favor  of  these  vases  having  been  the  true  porcelain  of 
China.  This  opinion  has,  however,  been  examined  with  con¬ 
siderable  industry  and  erudition  by  M.  l’abbe  le  Bland  and  M. 
Larcher,  in  two  dissertations,!  whereby  it  is  rendered  evident 
that  the  Vasa  Murrhina  were  formed  out  of  a  transparent  stone 
dug  from  the  earth  in  some  of  the  eastern  provinces  of  Asia.J 
There  is  abundant  evidence  to  show  that  Oriental  porcelain 
was  not  uncommon  in  Europe  during  the  first  century.  The 
pieces  of  this  manufacture  which,  according  to  Pliny,  were 
first  seen  in  Rome,  were  brought  there  from  Pontus  in  Asia, 
by  the  army  of  Pompey,  64  years  before  Christ. 


*  Nat.  Hist.  lib.  xxvii.  f  Mem.  de  Litterat.  tome  xliii. 

J  Robertson’s  Disquis.  concerning  India,  second  edit.  p.  387. 


CHAP.  I. 


HISTOKICAL  NOTICES. 


21 


Little  figures  covered  with  a  fine  deep-blue  glaze,  whicU 
are  found  deposited  with  Egyptian  mummies,  cause  it  to  ap¬ 
pear  that  porcelain  was  made  in  Egypt  in  very  ancient  times. 
It  is  a  curious  fact,  that  the  coloring  matter  wherewith  these 
figures  are  ornamented,  and  which  has  been  subjected  to  va¬ 
rious  chemical  tests,  affords  every  indication  of  its  being  oxide 
of  cobalt,  the  identical  substance  employed  for  the  same  pur¬ 
pose  by  the  European  porcelain  manufacturers  of  our  day,  but 
the  use  of  which  was  unknown  to  us  until  a  comparatively 
recent  period.  The  ore  of  cobalt  was  formerly  thrown  aside 
by  the  miners  of  Saxony  as  useless,  or  was  employed  only  in 
mending  roads.* 

The  Portuguese  traders  were  the  means  of  introducing  the 
fine  earthenwares  of  China  into  more  general  use  in  Europe ; 
and  the  name  assigned  to  the  fabric,  as  distinguishing  it  from 
the  coarser  descriptions  of  pottery  of  domestic  manufacture, 
was  most  probably  given  by  them — porcellana  signifying,  in 
the  Portuguese  language,  a  cup.  It  has  been  attempted  to  prove 
a  different  origin  for  the  name — attributing  this  to  the  resem¬ 
blance  which  the  glazing  or  varnish,  and  probably  the  colors, 
of  porcelain  bear  to  the  shells  used  in  some  parts  of  the  East 
instead  of  money  (couries),  and  which,  from  the  similarity  of 
their  shape  to  that  of  the  back  of  a  little  pig,  were  also  called 
porcella. 

The  possession  of  porcelain  vessels  afforded  but  little  insight 
into  the  nature  of  their  composition  or  the  mode  of  their  man¬ 
ufacture,  as  to  which  many  unfounded  theories  were  from 
time  to  time  proposed.  It  was  long  believed,  on  the  authority 
of  Cardan  and  the  elder  Scaliger — who,  although  violently 
opposed  to  each  other  on  various  and  more  important  subjects, 
yet  agreed  in  this — that  porcelain  was  made  from  a  mixture  of 


*  “  About  the  end  of  the  fifteenth  century,  cobalt  appears  to  have  been 
dug  up  in  great  quantity,  in  the  mines  on  the  borders  of  Saxony  and  Bohe¬ 
mia.  As  it  was  not  known  at  first  to  what  purpose  it  could  be  applied,  it 
was  thrown  aside  as  a  useless  mineral.  The  miners  had  an  aversion  to  it, 
not  only  because  it  gave  them  much  fruitless  labor,  but  because  it  often 
proved  prejudicial  to  their  health,  by  the  arsenical  particles  with  which  it 
was  combined  ;  and  it  appears  even  that  the  mineralogical  name  cobalt  then 
first  took  its  rise.  Frisch  derives  it  from  the  Bohemian  word  kow,  which 
signifies  metal ;  but  the  conjecture  that  it  was  formed  from  cobalus ,  which 
was  the  name  of  a  spirit  that,  according  to  the  superstitious  notions  of 
the  times,  haunted  mines,  destroyed  the  labors  of  the  miners,  and  often 
gave  them  a  great  deal  of  unnecessary  trouble,  is  more  probable.  The 
miners  perhaps  gave  this  name  to  the  mineral  out  of  joke,  because  it 
thwarted  them  as  much  as  the  supposed  spirit,  by  exciting  false  hopes  and 
rendering  their  labor  often  fruitless.  It  was  once  customary  to  introduce 
into  the  church  service  a  prayer,  that  God  would  preserve  miners  and  their 
works  from  Kobolts  and  spirits." — Beckmann,  Hist,  of  Inventions,  vol.  ii. 
pp.  341,  342. 


22 


PORCELAIN  MANUFACTURE. 


CHAP.  I. 


broken  egg  and  sea  shells,  which  were  preparatively  buried  in 
the  earth  for  nearly  a  hundred  years. 

It  was  not  until  the  beginning  of  the  18th  century  that  any 
light  was  thrown  upon  the  subject.  At  that  time,  the  Jesuit, 
Francis  Xavier  d’Entrecolles,  who  was  residing  as  a  missionary 
in  China,  contrived  to  elude  the  jealous  vigilance  so  generally 
practised  towards  strangers  in  that  country;  and  not  only  ob¬ 
tained  specimens  of  the  earths  used  in  the  composition  of  their 
porcelain,  but  also  acquired  some  knowledge  of  the  processes 
employed  in  the  manufacture  at  King-de-ching.  A  very  cir¬ 
cumstantial  letter  was  written  by  the  learned  father  on  the 
subject,  and  published  by  Grosier  in  his  general  description  of 
China :  but  owing  to  a  want  of  practical  knowledge  on  the 
part  of  D’Entrecolles,  his  descriptions  proved  so  defective  in 
many  particulars,  as  to  afford  little  or  no  assistance ;  besides 
which,  it  was  not  until  some  time  after  the  publication  of  his 
letter  that  any  substances  similar  to  the  earths  transmitted  by 
him  could  be  discovered  in  France. 

About  the  same  time,  and  while  the  acquisition  of  these 
Chinese  specimens  was  exciting  the  celebrated  Reaumur  to 
their  examination,  and  to  the  institution  of  a  series  of  experi¬ 
ments  which  will  be  hereafter  mentioned,  an  incidental  dis¬ 
covery  made  by  the  baron  de  Botticher,  a  German  alchemist, 
occasioned  the  establishment  of  the  porcelain  manufacture  in 
Saxony.  While  prosecuting  his  vain  experiments  in  search 
of  the  philosopher’s  stone,  this  man  prepared  some  crucibles, 
which  he  observed  were  caused  by  the  action  of  heat  to  assume 
all  the  characteristics  of  Oriental  porcelain.  Blinded  by  the 
avarice  which  prompted  their  visionary  labors,  the  adepts  of 
that  day  seem  generally  to  have  turned  away  from  the  im¬ 
portant  discoveries  that  courted  their  notice,  and  whicli  were 
thus  reserved  to  reward  the  patient  investigations  of  more  phi¬ 
losophic  minds  in  latter  times.  From  this  reproach  De  Botti¬ 
cher  is  free.  The  importance  of  the  real  discovery  thus  made 
was  sufficiently  apparent,  and  he  had  the  wisdom  to  abandon 
immediately  his  former  pursuit,  and  to  give  up  the  energies 
of  his  mind  to  the  establishment  of  a  manufacture,  which  was, 
in  the  end,  productive  of  more  beneficial  results  to  himself  and 
to  his  country,  than  if  he  had  indeed  been  successful  in  his 
alchemical  labors.  The  world  at  large  did  not  immediately 
reap  the  full  benefit  of  this  discovery,  as,  with  a  jealousy  but 
too  common,  the  processes  used  in  the  Dresden  works  were 
veiled  in  impenetrable  secrecy.  Up  to  tire  period  of  De  Bot- 
ticher’s  death,  in  1719,  only  white  porcelain  was  made  in 
Saxony;  yet  the  success  with  which  this  manufacture  was 
accompanied,  occasioned  attempts  at  imitation  in  France ;  and 


CHAP.  I. 


HISTORICAL  NOTICES. 


23 


porcelain  works  were  established  at  St.  Cloud,  and  in  the 
Fauxbourg  St.  Antoine  at  Paris — the  fabrics  produced  in  which, 
although  of  beautiful  external  appearance,  were  wanting  in 
most  of  the  qualities  essential  to  good  porcelain. 

The  investigations  of  Reaumur,  already  alluded  to,  were 
undertaken  with  more  rational  views,  and  prosecuted  with  a 
more  liberal  feeling.  The  result  of  his  researches  was  com¬ 
municated  by  him  to  the  Academy  of  Sciences,  and  published 
by  that  body  in  1727  and  1729.  Having  procured  specimens  of 
Oriental,  Saxon,  and  French  porcelains,  and  broken  them,  he 
proceeded  to  examine  their  internal  structure.  The  grain  in 
both  the  Chinese  and  Saxon  pieces  appeared  compact,  smooth, 
and  shining ;  while  that  of  the  French  ware  was  less  close  and 
fine,  without  lustre,  and  its  grain  resembled  sugar.  He  next 
proceeded  to  ascertain  their  habitudes  on  exposure  to  great 
heat  in  a  crucible,  and  reported,  that  all  the  European  speci¬ 
mens  were  melted,  while  that  of  China  remained  unaltered. 
This  most  essential  difference  led  Reaumur  to  discover  the 
true  nature  of  porcelain,  which  is  a  semi-vitrified  compound, 
in  which  one  portion  remains  infusible  at  the  greatest  heat  to 
which  it  can  be  exposed,  while  the  other  portion  vitrifies  at 
that  heat,  and  enveloping  the  infusible  part,  produces  that 
smooth,  compact,  and  shining  texture,  as  well  as  transparency, 
which  are  distinctive  of  true  porcelain.  Macquer,  in  his 
Chemical  Dictionary,  asserts,  that  Reaumur  was  wrong  in  class¬ 
ing  the  Saxon  manufacture  with  the  other  fusible  porcelains 
of  European  production ;  since  the  materials  of  which  it  is 
composed  have  always  been  similar  to  those  of  which  the  China 
ware  is  made,  one  portion  being  absolutely  infusible  during  the 
baking-. 

In  his  examination  of  the  two  porcelain  earths  received 
from  China,  which  are  called  in  that  country  pe-tun-tse  and 
kao-lin,  Reaumur  made  a  small  cake  of  each  substance,  sepa¬ 
rately,  and  exposed  both  to  the  heat  of  a  porcelain  furnace. 
One,  the  pe-tun-tse,  was  fused  by  this  means,  without  any  ad¬ 
dition  ;  while  the  other,  kao-lin,  gave  no  sign  of  fusion.  He 
next  intimately  compounded  the  two  earths,  and  found,  when 
the  mixture  was  baked,  that  it  had  acquired  all  the  qualities 
of  the  finest  Chinese  ware. 

All  that  was  then  wanting  for  the  perfect  imitation  of  this 
admired  production  was  the  discovery  of  materials  analogous 
to  the  specimen  furnished  by  D’Entrecolles.  The  search  for 
these  was  very  speedily  successful ;  and  the  manufacture  of 
porcelain  having,  from  this  time,  been  taken  under  the  royal 
patronage  in  France,  the  works  of  Sevres  produced  specimens 


24 


PORCELAIN  MANUFACTURE. 


CHAP.  I. 


of  art  which  vied  successfully  with  those  of  Dresden  and 
China. 

Mr.  Jonas  Hanway,  in  the  account  of  his  travels  published 
in  1753,  has  given  a  detailed  account  of  the  immense  collec¬ 
tion  of  porcelain  deposited  in  the  Chinese  palace  at  Dresden. 

“  The  vaults  of  this  palace,”  says  Mr.  Hanway,  “  consist  of 
fourteen  apartments  filled  with  Chinese  and  Dresden  porce¬ 
lain.  One  would  imagine  there  was  sufficient  to  stock  a  whole 
country ;  and  yet  they  say,  with  an  air  of  importance,  that  a 
hundred  thousand  pieces  more  are  wanted  to  complete  the  in¬ 
tention  of  furnishing  this  single  palace. 

“  Here  are  a  great  number  of  porcelain  figures  of  wolves, 
bears,  leopards,  &c. — some  of  them  as  big  as  the  life — a  pro¬ 
digious  variety  of  birds,  and  a  curious  collection  of  different 
flowers.  A  clock  is  preparing  for  the  gallery,  whose  bells  are 
to  be  also  of  porcelain :  I  heard  one  of  them  proved,  and  think 
they  are  sufficient  to  form  any  music ;  but  the  hammers  must 
be  of  wood. 

“  Here  are  forty-eight  large  China  vases,  which  appear  to 
be  of  no  use,  nor  any  way  extraordinary,  except  for  their  great 
size ;  and  yet  his  Polish  majesty  purchased  them  of  the  late 
king  of  Prussia  at  the  price  of  a  whole  regiment  of  dragoons.” 

One  part  of  this  collection  must  have  been  peculiarly  in¬ 
teresting,  as  it  exhibited,  in  an  orderly  arrangement,  specimens 
of  Dresden  manufacture  laid  up  by  this  king  of  Poland,  from 
the  first  efforts  of  De  Botticher,  through  every  subsequent 
gradation ;  “  an  idea,”  says  Mr.  Parke,  “  truly  philosophical, 
and  which  reflects  more  honor  on  his  memory  than  the  barter¬ 
ing  away  the  liberties  of  his  subjects  for  pieces  of  foreign 
porcelain.” 

Frederick  the  Great,  when  he  conquered  Saxony,  forcibly 
carried  away  several  of  the  best  workmen  from  the  manufac¬ 
tory  at  Meissen,  near  Dresden,  and  conveyed  them  to  Berlin, 
where,  since  that  time,  a  considerable  quantity  of  very  good 
porcelain  has  been  made  for  the  private  advantage  of  the  mon¬ 
arch.  As  many  as  500  men  are  constantly  employed  in  this 
establishment ;  but  although  much  of  their  material  is  drawn 
from  Saxony,  the  Prussian  porcelain  has  never  equalled  in 
quality  that  of  Dresden. 

It  is  generally  believed,  that  since  the  time  when  they  were 
first  established  by  the  Romans,  potteries  have  always  existed 
in  Staffordshire,  but  it  is  certain  that  until  the  beginning  of 
the  eighteenth  century  the  manufacture  was  confined  to  a 
few  objects  of  the  commonest  and  coarsest  description. 

The  district  in  this  county  wherein  the  great  bulk  of  Eng¬ 
lish  manufactured  earthenware  is  produced,  is  situated  about 


CHAP.  I.  HISTORICAL  NOTICES.  25 

a  mile  from  the  borders  of  Cheshire.  The  potteries  commence 
at  a  village  called  Golden  Hill,  and  extend  for  a  distance  of 
more  than  seven  miles,  passing  through  other  towns  and  vil¬ 
lages  to  Lane  End.  The  names  of  the  places  comprised  in 
this  district,  intermediate  between  the  two  already  mentioned, 
are  Newfield,  Smithfield,  Tunstall,  Longport,  JBurslem,  Co¬ 
bridge,  Etruria,  Hanley,  Shelton,  Stoke,  Lower  Lane,  and 
Lower  Delf.  All  these  have  formerly  been  sufficiently  dis¬ 
tinct  from  each  other ;  but  the  increase  of  the  staple  manufac¬ 
ture  of  the  district  has  called  for  the  erection  of  so  many  new 
potteries  and  dwelling-houses,  that  their  individuality  has  been 
lost,  and  to  a  stranger  the  whole  presents  very  much  the  ap¬ 
pearance  of  one  large  town.  In  every  part  of  the  kingdom, 
except  the  district  itself,  the  whole  are  ranked  under  one 
general  name — that  of  the  Potteries.  Etruria  is  the  creation 
of  the  celebrated  Josiah  Wedgwood,  by  whom  the  place  was 
thus  named  after  one  of  the  ancient  Italian  states,  celebrated 
for  the  tasteful  forms  it  gave  to  its  pottery,  specimens  of  which 
have  materially  promoted  the  improvement  of  our  modern 
English  wares. 

In  the  year  1686,  when  Dr.  Plot  published  a  Natural  His¬ 
tory  of  Staffordshire,  its  traffic  in  earthenware  was  very  unim¬ 
portant — being  carried  on  only  by  the  workmen  themselves, 
or  by  pedlars,  who  conveyed  the  pieces  in  baskets  on  their 
backs  through  the  adjoining  counties.  About  the  time  just 
mentioned  (1690),  two  brothers,  named  Elers,  came  from  Nu¬ 
remberg,  in  Holland,  and  settled  at  Bradwell,  where  they 
made  an  improved  kind  of  red  ware,  and  introduced  the  art 
of  glazing  the  vessels  by  throwing  common  salt  into  the  oven 
at  a  certain  period  of  the  baking*  Every  precaution  was 
used  by  the  brothers  to  keep  their  processes  secret ;  and  it  is 
probable  that  this  circumstance,  joined  to  the  success  of  the 
strangers,  excited  the  enmity  and  jealousy  of  their  neighbors 
to  the  degree  which  obliged  them  to  leave  the  country.  The 
pretext  assigned  for  this  persecution  was  the  alarm  occasioned 
by  the  fumes  from  their  kilns  during  the  time  of  glazing.  These 
fears  subsided,  however,  when  the  process  was  continued  by 
their  successor.  This  man,  whose  name  was  Astbury,  had,  it 
is  said,  become  master  of  their  secrets  by  a  singular  stratagem. 
Feigning  to  be  of  weak  intellect,  and  assuming  an  appropriate 
vacuity  of  countenance,  he  obtained  employment  in  the  Brad- 
well  works,  and  submitted  to  all  the  drudgery  and  contumely 
which  were  drawn  upon  him  by  his  supposed  imbecility.  By 


*  The  salt  is  decomposed  by  this  means ;  and,  rising  in  fumes,  the  alkali 
which  it  contains  combines  with  the  silica  of  the  ware,  and  forms  a  true 
glass  which  covers  the  entire  surface. 

c 


26 


PORCELAIN  MANUFACTURE. 


CHAP.  I. 


this  course  of  proceeding,  he  was  enabled,  unsuspected,  to 
acquire  a  knowledge  of  all  that  was  done  in  the  manufactory, 
and  to  make  models  for  his  own  use  of  all  the  utensils. 

The  advantages  of  this  method  of  glazing  with  salt  were  so 
apparent,  that  in  a  short  time  it  was  very  generally  adopted  ; 
and  on  Saturday,  the  day  appropriated  to  this  process,  the 
thick  fumes  from  nearly  sixty  potteries  filled  the  towns  to  a 
degree  which  darkened  the  atmosphere,  and  covered  the  hills 
of  the  surrounding  district.* 

To  Astbury  is  generally  ascribed  the  introduction  of  white 
stone-ware,  by  the  adoption  of  calcined  flints  in  its  composition. 
The  popular  version  of  the  origin  of  this  improvement  states, 
that  “  while  travelling  to  London  on  horseback,  in  the  year 
1720,  Astbury  had  occasion,  at  Dunstable,  to  seek  a  remedy 
for  a  disorder  in  his  horse’s  eyes ;  when  the  ostler  at  the  inn, 
by  burning  a  flint,  reduced  it  to  a  fine  powder,  which  he  blew 
into  them.  The  potter,  observing  the  beautiful  white  color 
of  the  flint  after  calcination,  instantly  conceived  the  use  to 
which  it  might  be  applied  in  his  art.”f 

The  merit  of  this  man  has  been  somewhat  overlooked, 
while  contemplating  the  greater  claims  to  admiration  possessed 
by  his  more  philosophic  successor  in  the  course  of  improvement. 
That  could  have  been  no  common  mind,  however,  which  led 
Astbury  to  the  long-continued  pursuit  of  his  object,  by  means 
so  humiliating;  and  which  also  enabled  him,  on  the  occasion 
just  related,  to  seize  upon  a  fact  thus  accidentally  presented, 
and  which,  although  of  high  importance  to  his  art,  might  have 
passed  unheeded  before  the  eyes  of  many  a  common-place 
manufacturer. 

The  step  thus  made  was  of  consequence  in  preparing  the 
way  for  the  far  greater  advances  towards  perfection,  after¬ 
wards  accomplished  by  Mr.  Josiah  Wedgwood.  This  extra¬ 
ordinary  man  owed  none  of  his  success  to  fortuitous  circum¬ 
stances.  Devoting  his  mind  to  patient  investigations,  and 
sparing  neither  pains  nor  expense  in  accomplishing  his  aims, 
he  gathered  round  him  talented  artists  from  different  countries, 
and  drew  upon  the  stores  of  science  for  aid  in  pursuing  the  ob¬ 
jects  of  his  praiseworthy  ambition.  The  early  and  signal 
prosperity  whereby  his  efforts  were  attended,  served  only  as  a 
motive  urging  him  forward  to  new  exertions,  and  as  the  means 
for  calling  forth  and  encouraging  talents  in  others,  in  a  manner 
calculated  to  promote  the  welfare  of  his  country.  Previously 
to  his  time,  the  potteries  of  Staffordshire  produced  only  inferior 
fabrics,  flimsy  as  to  their  materials,  and  void  of  taste  in  their 


*  Parke,  Ohein.  Cat.  p.  125. 


t  Parke,  Chem.  Cat.  p.  126. 


CHAP.  I. 


HISTORICAL  NOTICES. 


27 


forms  and  ornaments — the  best  among  them  being  only 
wretched  imitations  of  the  grotesque  and  unmeaning  scenes 
and  figures  portrayed  on  the  porcelain  of  China.  But  such 
have  been  the  effects  resulting  from  the  exertions  and  exam¬ 
ple  of  this  one  manufacturer,  that  the  wares  of  that  district 
are  now  not  only  brought  into  general  use  in  this  country,  to 
the  exclusion  of  all  foreign  goods,  which  had  before  been 
largely  imported,  but  English  pottery  has  since  been  sought 
for  and  celebrated  throughout  the  civilized  world,  and  adopted 
even  in  places  where  the  art  was  previously  prosecuted.  An 
intelligent  foreigner,  M.  Faujas  de  Saint  Fond,  writing  on  this 
subject,  says,  “  its  excellent  workmanship,  its  solidity,  the  ad¬ 
vantage  which  it  possesses  of  sustaining  the  action  of  fire,  its 
fine  glaze  impenetrable  to  acids,  the  beauty  and  convenience 
of  its  form,  and  the  cheapness  of  its  price,  have  given  rise  to 
a  commerce  so  active  and  so  universal,  that  in  travelling  from 
Paris  to  Petersburgh,  from  Amsterdam  to  the  further  part  of 
Sweden,  and  from  Dunkirk  to  the  extremity  of  the  south  of 
France,  one  is  served  at  every  inn  upon  English  ware. 
Spain,  Portugal,  and  Italy,  are  supplied  with  it ;  and  vessels 
are  loaded  with  it  for  the  East  Indies,  the  West  Indies,  and 
the  continent  of  America.”* 

It  is  not  among  the  least  of  Mr.  Wedgwood’s  merits,  that 
he  overcame  the  disadvantages  of  a  defective  education  ;  and, 
amid  the  calls  of  an  incessantly  active  life,  found  time  wherein 
to  school  his  mind  in  all  the  discipline  necessary  for  investiga¬ 
tions  purely  scientific.  The  ample  fortune  which  he  acquired 
was  ever  ready  for  promoting  the  spread  of  knowledge,  en¬ 
couraging  the  efforts  of  genius,  and  lessening,  as  far  as  possi¬ 
ble,  the  sufferings  of  his  fellow-creatures.  His  charities,  pub¬ 
lic  and  private,  and  especially  in  his  own  district,  were  ex¬ 
emplary  and  consistent.  He  gave  life  to  many  objects  of 
public  utility.  The  Trent  and  Mersey  canal  was  undertaken 
and  accomplished  through  his  influence ;  and  by  the  benefits 
it  has  produced  to  the  district,  and  to  its  proprietors,  has  fully 
approved  his  wisdom  in  its  promotion. 

The  principal  inventions  of  Mr.  Wedgwood  were — 1.  His 
table  ware ;  the  merits  of  which  are,  that  it  has  a  dense  and 
durable  body,  and  is  covered  with  a  brilliant  glaze,  capable  of 
bearing  uninjured  sudden  and  great  vicissitudes  of  heat  and 
cold.  This  ware,  as  it  was  capable  of  being  manufactured 
with  ease  and  expedition,  could  be  sold  at  a  cheap'  rate,  and 
would  still  yield  a  handsome  profit  to  the  inventor.  Its  va¬ 
rious  qualities,  so  superior  to  any  possessed  by  previous  manu- 


*  Travels  in  England  and  Scotland  (English  translation,)  vol,  i.  p.  97 


28  PORCELAIN  MANUFACTURE.  CHAP.  I. 

factures  of  either  domestic  or  foreign  production,  caused  this 
ware  to  be  taken  into  immediate  and  universal  favor  with  the 
public.  Among  others,  the  queen  bestowed  upon  it  the  tribute 
of  her  admiration  and  patronage  ;  commanded  it  to  be  called 
queen's  ware — a  name  which  it  continues  to  bear  to  the  pres¬ 
ent  day ;  and  honored  Mr.  Wedgwood  by  appointing  him  her 
majesty’s  potter. 

2.  A  terra  cotta ,  which  could  be  made  to  resemble  por¬ 
phyry,  granite,  Egyptian  pebble,  and  other  beautiful  stones  of 
the  silicious  or  chrystalline  order. 

3.  Basaltes,  or  black  ware.  This  was  a  black  porcelainous 
biscuit,  having  nearly  the  same  properties  with  the  natural 
stone.  It  would  emit  sparks  when  struck  with  steel;  was 
capable  of  taking  a  high  polish ;  resisted  acids ;  and  would 
bear,  without  injury,  a  stronger  degree  of  heat  than  even  the 
natural  basaltes. 

4.  White  porcelain  biscuit.  This  ware  had  a  smooth,  wax¬ 
like  appearance,  and  was  possessed  of  all  the  properties  ex¬ 
hibited  by  the  preceding  invention,  differing  from  it  only  in 
regard  to  its  color. 

5.  Bamboo,  or  cane-colored  porcelain  biscuit,  of  the  same 
nature  as  the  preceding. 

6.  Jasper.  This  was  also  a  white  porcelainous  biscuit,  of 
exquisite  delicacy  and  beauty,  having  in  general  all  the  prop¬ 
erties  of  the  basaltes,  with  this  in  addition, — that  it  would  re¬ 
ceive  through  its  whole  substance,  from  the  admixture  of 
metallic  oxides,  the  same  colors  as  those  oxides  communi¬ 
cate  to  glass  or  enamel  in  fusion.  This  peculiar  property, 
which  it  shares  with  no  other  porcelain  or  earthenware  body 
of  either  ancient  or  modern  composition,  renders  it  applicable 
in  a  very  pleasing  manner  to  the  production  of  cameos,  por¬ 
traits,  and  all  subjects  that  require  to  be  shown  in  bas-relief ; 
since  the  ground  can  be  made  of  any  color  that  may  be  pre¬ 
ferred  ;  while  the  raised  figures  are  of  the  purest  white. 

7.  A  porcelain  biscuit,  possessing  several  properties  that 
render  it  invaluable  to  the  chemist,  and  which  have  occasioned 
this  invention  to  be  brought  into  general  use  in  all  laboratories. 
The  ware  is  exceedingly  hard,  being  little  inferior  in  this  re- 
pect  to  agate,  whence  it  is  peculiarly  adapted  for  forming 
mortars.  It  resists  the  action  of  the  strongest  acids  and  of  all 
corrosive  substances,  and  has  the  further  quality  of  being  per¬ 
fectly  impenetrable  by  any  known  liquid. 

The  investigations  of  Reaumur,  already  detailed,  make  it 
evident  that  the  characteristics  of  porcelain,  as  far  as  they  de¬ 
pend  upon  semi-vitrification,  may  be  obtained  when  ingre¬ 
dients  wholly  fusible  are  employed,  provided  the  fire  be  care- 


chap.  i. 


HISTORICAL  NOTICES. 


29 


fully  withdrawn  from  the  oven  at  the  precise  moment  when 
vitrification  has  arrived  at,  and  not  proceeded  beyond,  a  certain 
point.  Accordingly,  this  porcelain  was,  at  one  time,  very  com¬ 
monly  produced  both  in  this  and  other  countries.  The  quality 
of  goods  thus  composed  is  always  inferior  to  that  of  true  porce¬ 
lain  ;  and,  if  further  or  again  exposed  to  the  heat  of  the  fur¬ 
nace,  the  substance  would  entirely  change  its  nature,  and  run 
into  a  vitreous  and  shapeless  mass. 

Porcelain  of  this  description,  much  esteemed  for  its  beauty, 
was  long  manufactured  at  Bow  and  at  Chelsea.  It  was  not 
until  the  year  1768,  that  Mr.  Cookworthy  discovered  certain 
mineral  substances  in  Cornwall  similar  in  their  properties  to 
the  porcelain  earths  of  China ;  and  having  secured  to  himself, 
by  patent,  the  exclusive  right  of  using  those  materials,  was  the 
first  person  who  made  true  porcelain  in  England. 

In  practising  this  art,  Mr.  Cookworthy,  and  those  to  whom 
he  afterwards  assigned  his  patent  right,  attained  to  considerable 
success  as  regarded  the  quality  of  their  manufactures,  although 
the  demand  for  their  goods  did  not  prove  proportionate  to  the 
money  expended  in  bringing  the  processes  to  perfection.  One 
probable  cause  for  the  inadequacy  of  their  remuneration,  ex¬ 
isted  in  the  successful  efforts  of  Mr.  W edgwood,  which  have 
been  already  detailed,  for  improving  the  quality  of  common 
earthenwares  made  in  Staffordshire,  whereby  foreign  porcelain 
was  rendered  less  an  object  of  desire,  and  consequently  its  suc¬ 
cessful  imitation  was  no  longer  considered  as  being  of  any 
great  importance. 

The  extent  to  which,  in  the  year  1785,  this  manufacture  had 
arrived,  and  its  importance  to  the  three  great  interests  of  the 
country — landed,  maritime,  and  commercial — may  be  collected 
from  the  evidence  then  given  by  Mr.  Wedgwood  before  a  com¬ 
mittee  of  the  privy-council,  and  at  the  bars  of  the  two  houses 
of  parliament.  The  question  at  that  time  under  the  considera¬ 
tion  of  the  legislature,  and  upon  which  these  examinations 
were  taken,  arose  out  of  the  proposal  of  government  to  abolish 
the  system  of  commercial  restrictions  and  disabilities  then  ex¬ 
isting  between  Great  Britain  and  Ireland,  and  to  render  the 
intercourse  between  the  two  divisions  of  the  empire  nearly  as 
free  and  unrestricted  as  that  between  the  counties  of  Durham 
and  Northumberland;  a  proposition  so  perfectly  natural  and 
reasonable  in  itself,  that,  but  for  the  possession  of  records 
wherein  they  have  been  preserved,  we  might  really  be  at  a 
loss  to  conjecture  the  nature  of  the  arguments  whereby  it  was 
opposed  and  defeated. 

In  the  course  of  the  discussions  to  which  this  subject  gave 
rise  in  the  house  of  lords,  the  marquess  of  Lansdowne,  remark- 

C  2 


30 


PORCELAIN  MANUFACTURE. 


CHAP.  I. 


ing  upon  the  evidence  given  by  the  respectable  merchants  and 
manufacturers  at  the  bar  of  the  house,  declared  that  the  result 
to  which  he  in  his  own  mind  had  arrived  was  the  very  opposite 
to  the  conviction  which  they  had  adopted.  “  Though  much 
valuable  information  may,”  said  his  lordship,  “  doubtless,  be  de¬ 
rived  from  their  evidence,  it  must  not  be  forgotten  that  they  are 
men  peculiarly  subject  to  prejudice  and  error,  in  all  cases 
where  their  personal  interests  are  concerned.  Were  any  one, 
for  instance,  to  ask  a  manufacturer  of  Halifax,  what  is  the 
greatest  crime  upon  earth  1  Is  it  felony,  is  it  murder,  is  it  par¬ 
ricide  I  No  !  he  would  answer ;  it  is  none  of  these — it  is  the 
exporting  of  wool.” 

In  later  times,  we  have  seen  this  measure  of  justice  and 
sound  policy  more  successfully  brought  forward  ;  and  it  is  ac¬ 
knowledged  that  each  country  has  since  been  reaping  benefits 
in  consequence,  upon  the  inevitable  arrival  of  which  nothing 
but  the  strongest  commercial  prejudices  and  national  jealousy 
could  have  thrown  even  a  momentary  doubt. 

Mr.  Wedgwood,  in  the  course  of  the  evidence  already  al¬ 
luded  to,  thus  remarks  : — “  Though  the  manufacturing  part 
alone  in  the  Potteries,  and  their  immediate  vicinity,  gives  bread 
to  15  or  20,000  people,  yet  this  is  but  a  small  object  when  com¬ 
pared  with  the  many  others  which  depend  on  it ;  namely,  1st, 
The  immense  quantity  of  inland  carriage  it  creates  throughout 
the  kingdom,  both  for  its  raw  materials  and  finished  goods. 
2d,  The  great  number  of  people  employed  in  the  extensive 
collieries  for  its  use.  3d,  The  still  greater  number  employed 
in  raising  and  preparing  its  raw  materials  in  several  distant 
parts  of  England,  from  near  the  Land’s  End,  in  Cornwall — one 
way  along  different  parts  of  the  coast,  to  Falmouth,  Teignmouth, 
Exeter,  Pool,  Gravesend,  and  the  Norfolk  coast ;  the  other 
way  to  Biddeford,  Wales,  and  the  Irish  coast.  4th,  The  coast¬ 
ing  vessels,  which,  after  having  been  employed  at  the  proper 
season  in  the  Newfoundland  fishery,  carry  these  materials 
coastwise  to  Liverpool  and  Hull,  to  the  amount  of  more  than 
20,000  tons  yearly ;  and  at  times  when,  without  this  employ¬ 
ment,  they  would  be  laid  up  idle  in  harbor.  5th,  The  further 
conveyance  of  these  materials  from  those  ports,  by  river  and 
canal  navigation,  to  the  Potteries,  situated  in  one  of  the  most 
inland  parts  of  this  kingdom  ;  and,  6th,  The  reconveyance  of 
the  finished  goods  to  the  different  parts  of  this  island,  where 
they  are  shipped  for  every  foreign  market  that  is  open  to  the 
earthenwares  of  England.” 

Mr.  Wedgwood  very  justly  observed  further,  that  this  manu¬ 
facture  is  attended  with  some  circumstances  of  advantage 
which  are  almost  peculiar  to  itself ;  viz.  that  the  value  of  the 


CHAP.  I. 


HISTORICAL  NOTICES. 


31 

finished  goods  consists  almost  wholly  in  the  labor  bestowed 
upon  them;  that  every  ton  of  raw  materials  produces  several 
tons  of  merchandise  for  shipping,  the  freight  being  paid,  not 
upon  the  weight,  but  according  to  the  bulk ;  that  scarcely  a 
vessel  leaves  any  of  our  ports  whose  lading  is  not  in  part  made 
up  of  these  cheap,  bulky,  and,  for  these  reasons,  valuable  articles, 
to  this  maritime  country ;  and  that  fully  five  parts  in  six  of  the 
aggregate  manufactures  of  the  Potteries  are  exported  to  foreign 
markets. 

Important  as  were  the  advances  which  at  that  time  had  been 
made  in  the  art,  Mr.  Wedgwood  was  still  of  opinion  that  they 
could  be  considered  but  as  the  beginning  of  improvements, — 
that  these  were  still  but  in  their  infancy,  and  but  of  little  mo¬ 
ment  when  compared  with  those  to  which  the  art  was  capable 
of  attaining,  through  the  continued  industry  and  growing  in¬ 
telligence  of  the  manufacturers,  in  combination  with  and  fostered 
by  the  natural  facilities  and  political  advantages  enjoyed  by  the 
country ;  an  opinion  fully  borne  out  by  the  event,  and  which 
our  progressive  experience  shows  to  have  been  founded  on  clear 
and  accurate  perceptions. 

The  manufacture  of  earthenwares  in  England  is  far  from 
being  restricted  to  the  district  in  Staffordshire  which  has  been 
described  already  as  having  acquired  the  name  of  “the  Pot¬ 
teries.”  Establishments  for  making  the  commoner  kinds  of 
wares  are  to  be  found  in  many  and  various  parts  of  the  king¬ 
dom;  at  Lambeth,  especially,  several  manufactories  of  stone 
pottery  have  been  carried  on  for  considerably  more  than  a  cen¬ 
tury,  producing  articles  which  have  never  been  surpassed  in 
any  country,  either  for  the  excellence  of  their  materials  and 
workmanship,  or  for  the  magnitude  of  the  vessels  and  the  va¬ 
riety  of  uses  to  which  they  are  adapted.  The  Lambeth  ware 
may,  in  fact,  be  pronounced  perfect  of  its  kind. 

Porcelain  has  long  been  made  at  Derby,  and  at  Coalport, 
near  Colebrook  Dale,  in  Shropshire.  Establishments  have  sub¬ 
sequently  risen  in  the  city  of  Worcester,  wherein  very  beauti¬ 
ful  specimens  are  produced  ;  and  yet  more  recently,  the 
manufacture  of  excellent  porcelain  has  been  engrafted  upon  a 
long-established  pottery  for  commoner  wares,  situated  at  Swin- 
ton,  near  Rotherham,  in  Yorkshire.  At  the  Rockingham 
works,  which  have  been  so  named  in  compliment  to  their  early 
patron,  the  celebrated  marquess  of  Rockingham,  porcelain  is 
now  produced  which  vies  successfully  in  every  kind  of  excel¬ 
lence  with  that  of  older  English  establishments.  Among  many 
other  specimens  which  attest  the  proficiency  of  the  Yorkshire 
manufacturers,  two  may  be  more  particularly  mentioned,  which 
are  deserving  of  more  than  common  attention  as  denoting  the 


32 


PORCELAIN  MANUFACTURE. 


CHAP.  I. 


degree  of  advancement  to  which  the  art  lias  reached  in 
England. 

One  of  these  pieces  is  a  copy  in  enamel  colors,  made  on  a 
porcelain  tablet,  from  an  original  painting  by  Vandyke,  and 
now  in  the  possession  of  the  noble  inhabitant  of  Wentworth 
Castle.  The  subject  of  the  picture  is,  “  The  earl  of  Strafford 
occupied  in  dictating  his  defence  to  his  secretary.”  The  exe¬ 
cution  of  this  copy  does  justice  to  the  masterly  original;  and, 
in  regard  to  expression  and  coloring,  has  been  pronounced  equal 
to  the  most  admired  productions  of  the  Sevres  works.  The 
other  specimen  is  remarkable  not  only  for  elegance  of  design, 
and  the  goodness  of  the  workmanship,  but  also  because  it  is 
believed  to  be  the  largest  piece  of  porcelain  that  has  hitherto 
been  made  in  this  country.  It  is  a  scent-jar,  forty-four  inches 
high,  made  and  fired  in  one  entire  piece.  The  base,  or  plinth, 
is  triangular,  having  a  circular  projection  at  each  angle;  from 
these  rise  lions’  paws,  upon  which  the  globular  body  of  the  jar 
is  supported.  The  scent  is  allowed  to  escape  through  hexag¬ 
onal  openings  in  the  neck.  The  jar  is  divided  into  three  com¬ 
partments,  by  as  many  rustic  handles  of  knotted  oak ;  while 
branches  of  the  same  tree,  wfith  their  rich  foliage  rising  from 
the  plinth,  are  spread  tastefully  over  the  lions’  paws,  and  thence 
entwining  with  the  handles,  rise  and  encircle  the  base  of  the 
neck.  The  ornaments  of  the  cover  are  in  keeping  with  those 
of  the  jar,  it  being  covered  with  branches  and  foliage  of  the 
oak :  the  whole  is  surmounted  by  the  figure  of  a  rhinoceros. 
The  three  compartments  into  which  the  jar  is  divided  are  en¬ 
riched  with  highly  finished  paintings  in  enamel  colors,  executed 
by  one  of  the  proprietors  of  the  works,  from  designs  by  Stothard, 
the  subjects  of  which  are  drawn  from  the  admirable  romance 
of  Cervantes.  The  circular  projections  at  the  base,  and  the 
cover,  are  adorned  with  paintings  from  nature,  of  six  subjects 
of  rare  botanical  plants,  the  originals  of  which  are  in  the  con¬ 
servatories  of  Wentworth  Castle.  The  whole  is  relieved  and 
enlivened  by  ornamental  work,  in  burnished  and  chased  gold ; 
and  the  work,  both  in  its  design  and  execution,  is  highly  honor¬ 
able  to  the  artists. 

Up  to  a  comparatively  recent  period,  the  manufacture  of 
earthenwares  formed  one  of  the  very  few  branches  of  domestic 
industry  which  were  left  free  from  the  evil  effects  of  direct 
taxation,  and,  except  in  one  branch,  of  very  minor  importance, 
the  art  is  still  in  the  enjoyment  of  this  immunity;  to  which  fa¬ 
vorable  circumstance  may  be  imputed  much  of  the  signal  and 
uniform  success  whereby  it  has  been  attended.  In  the  year 
1812,  when  the  duty  upon  glass  bottles  was  doubled,  the  manu¬ 
facturers  of  these  represented  to  the  chancellor  of  the  ex- 


CHAP.  I. 


HISTORICAL  NOTICES. 


33 


chequer,  that  unless  a  countervailing  tax  was  levied  upon  stone 
bottles,  the  latter,  being  wholly  unburthened,  would  possess  an 
unfair  advantage,  and  might  be  sold  at  prices  that  would  drive 
glass  bottles  out  of  use.  This  was  a  line  of  argument  in  no 
wise  unpalatable  to  the  minister,  who  readily  caught  at  the 
suggestion  of  a  new  object  for  taxation ;  and  a  duty  of  five 
shillings  on  each  hundredweight  was  immediately  imposed  upon 
all  stone  bottles  the  content  of  which  should  be  two  quarts  and 
under. 

The  levying  of  this  duty  calls  for  the  attendance  of  revenue 
officers  at  all  hours  on  the  premises  of  every  stoneware  manu¬ 
facturer  throughout  the  kingdom ;  and  it  is  very  much  to  be 
doubted  whether,  in  any  one  year  since  its  first  imposition,  the 
expenses  of  collection  have  not  more  than  absorbed  the  whole 
amount  paid  by  the  potters.  The  total  quantity  of  stoneware 
made  which  is  chargeable  with  the  duty  does  not  exceed  600 
tons  annually,  and  a  large  proportion  of  this  is  used  for  purposes 
to  which  glass  has  never  been  applied.  It  is  not  very  likely 
that  stoneware,  the  utility  of  which  for  many  purposes  is  ex¬ 
ceedingly  great,  would  ever  have  been  brought  into  competi¬ 
tion  with  a  material  so  much  lighter,  and  in  many  respects  so 
much  more  convenient,  even  had  the  pottery  continued  free 
from  the  domiciliary  visits  of  the  exciseman ;  and  now  that  the 
experiment  has  been  fairly  tried  during  nearly  twenty  years, 
and  has  been  found  unproductive  of  any  real  revenue,  there 
can  be  no  sufficient  reason  for  continuing  the  impost. 


CHAP.  H. 

GENERAL  DESCRIPTION  OF  INGREDIENTS  USED  IN  THE  MANU¬ 
FACTURE. 

Different  branches  of  the  art. — Ingredients  used. — Properties  of  Alumina. — 
Its  infusibility. — Contraction  when  exposed  to  heat. — Wedgwood's  Pryom- 
eter. — Composition  of  Gems. — Great  abundance  of  Clay. — Properties  of  Si¬ 
lica. — Its  great  abundance. — Sea  sand. — Incapable  of  artificial  solution  in 
water. — Dissolved  naturally. —Springs  at  Carlsbad.— Boiling  fountain  in 
Iceland. — Fusion  of  Silex. — Kinds  of  Clay  used  in  Potteries. — Their  vari¬ 
ous  merits. — China  clay  of  Cornwall. — Mode  of  its  preparation. — Its  anal¬ 
ysis. — Cornish  Felspar. — Its  fusibility. — Steatile. — Earth  of  Baudissero. — 
Its  analysis. — Cornish  sopestone. — Spuma  maris. — Its  employment  in  por¬ 
celain  works  in  Spain.  * 

The  art  of  manufacturing  pottery  and  porcelain  naturally 
divides  itself  into  four  different  and  distinct  branches :  the  first 
of  these  comprehends  a  knowledge  of  the  nature  and  peculiar 
properties  of  the  various  materials,  whereof  the  vessels  are 
composed ;  the  second  comprises  the  methods  used  in  combining 
these  materials,  and  in  fashioning  the  vessels;  the  third  branch 


34 


PORCELAIN  MANUFACTURE. 


CHAP.  II. 


includes  the  choice  and  management  of  the  colors  and  enamels 
employed  in  painting  and  ornamenting  the  wares,  together  with 
the  operations  necessary  for  their  conversion ;  and  the  last  di¬ 
vision  embraces  the  means  required  for  completing  the  manu¬ 
facture  by  the  aid  of  fire.  In  describing,  however,  the  different 
stages  of  the  manufacture  as  they  occur,  the  painting  and  baking 
processes  must  unavoidably  be  intermingled. 

The  chief  ingredients  employed  in  the  composition  of  all  kinds 
of  pottery  are  clay  and  flint:  these  are  both  classed  by  chemists 
among  the  primitive  earths.  The  first  of  them,  in  its  state  of 
purity,  is  denominated  alumina,  or  oxide  of  aluminum ;  and  the 
latter  is  called  silica,  or  oxide  of  silicium.  It  is  only  since  the 
year  1754  that  alumina  has  been  acknowledged  as  a  peculiar 
substance ;  and  the  period  is  much  more  recent  when  the  re¬ 
searches  of  Davy  proved  it  to  belong  to  the  class  of  metallic 
oxides. 

It  is  of  great  importance  to  make  choice  of  a  suitable  kind  of 
clay  for  the  manufacture ;  but,  according  to  the  remark  of  the 
celebrated  Vauquelin,  it  is  much  more  important  to  combine 
this  with  a  due  proportion  of  flint,  as  good  pottery  differs  from 
that  which  is  inferior  less  in  the  original  quality  of  its  elements 
than  in  their  proportions. 

Clay  is  an  opaque  and  non-crystallized  body,  of  dull  fracture, 
soft  enough  in  all  states  to  take  a  mark  from  iron ;  when 
breathed  on  it  exhales  an  odor  which,  from  its  peculiarity,  takes 
its  name  from  the  material,  and  is  termed  argillaceous.  This 
is  owing  to  the  oxide  of  iron  which  is  mixed  with  it,  as  clay, 
when  absolutely  pure,  does  not  emit  any  odor.  Clay  forms  with 
water  a  plastic  paste,  having  considerable  tenacity,  and  which, 
by  the  action  of  heat,  is  brought  to  a  very  great  degree  of  hard¬ 
ness  :  it  is  compact,  smooth,  and  almost  unctuous  to  the  touch, 
and  when  dry,  may  be  easily  polished  by  the  finger.  It  is  not 
soluble  in  water,  but  mixes  readily  with  it  in  all  proportions, 
parting  with  difficulty  from  the  last  portion  of  that  which  it  has 
absorbed:  it  will  adhere  to  the  tongue.  The  description  of  clay 
employed  by  potters  is  infusible  in  the  heat  of  a  porcelain  fur¬ 
nace,  where  some  kinds,  owing  to  their  being  combined  with 
oxide  of  iron,  assume  a  red  color,  while  others  become  of  a  pure 
white.  The  highest  temperature  to  which  clay  can  be  exposed 
tends  only  to  increase  its  density,*  hardening  its  substance  and 
diminishing  its  volume.  This  diminution  of  volume  produced 
by  increased  temperature  is  an  apparent  deviation  from  the 
general  law  of  expansion  by  heat ;  but  the  deviation  is  only  ap¬ 
parent,  and  is  probably  produced  by  the  vaporization  of  liquid, 
combined  with  the  clay.  Mr.  Wedgwood  found  that  the  dimi¬ 
nution  of  volume  produced  by  exposing  the  clay  to  these  ex- 


CHAP.  XI. 


Wedgwood’s  pyrometer. 


35 


treme  temperatures,  continued  the  same  after  the  clay  was  suf¬ 
fered  to  cool,  and  therefore  that  its  amount  admitted  of  delib¬ 
erate  and  accurate  measurement.  He  also  supposed  (though  er¬ 
roneously)  that  the  shrinkage  of  the  clay  was  always  propor¬ 
tional  to  the  temperature  to  which  it  had  been  exposed.  This 
led  to  his  well-known  invention  of  the  pyrometer,  an  instru¬ 
ment  for  measuring  degrees  of  temperature  beyond  the  range 
of  the  common  thermometer.  The  instrument  consisted  of 
small  cylinders,  composed  of  two  parts  of  the  porcelain  clay  of 
Cornwall,  and  one  part  of  pure  alumina.  These,  when  baked 
in  a  low  red  heat  and  then  cooled,  were  constructed  of  such  a 
size  as  just  to  enter  between  the  wider  extremities  of  two 
brass  rods,  fixed  on  a  plate  twenty-four  inches  long,  half  an 
inch  asunder  at  one  end,  and  three-tenths  of  an  inch  at  the 
other.  These  rods  were  divided  to  tenths  of  an  inch,  and  con¬ 
sequently  each  division  formed  the  240th  part  of  the  whole 
length.  The  clay  cylinders,  being  exposed  to  the  heat  which 
was  required  to  be  determined,  were  subsequently  inserted  be¬ 
tween  these  bars,  and  by  reason  of  their  contraction  they  ad¬ 
vanced  between  them  to  a  point  depending  on  the  amount  of 
their  shrinkage. 

This  pyrometer,  however,  has  been  found  to  be  subject  to  a 
fatal  defect.  The  shrinkage  of  the  clay  does  not  depend  on 
the  temperature  alone  of  the  fire  to  winch  it  is  exposed,  but 
also  on  the  length  of  time  which  the  fire  has  acted  upon  it. 
Thus  a  lesser  degree  of  heat  will  produce  the  same  shrinkage 
as  a  greater  degree,  provided  the  clay  is  exposed  to  the  former 
for  a  longer  portion  of  time.  The  instrument  has  been,  conse¬ 
quently,  long  since  totally  laid  aside. 

Some  of  the  most  valued  among  the  precious  stones,  such  as 
rubies,  sapphires,  emeralds,  jaspers,  and  others,  are  composed 
of  either  alumina  or  silica,  or  of  the  two  earths  in  combination, 
together  with  different  small  portions  of  lime,  or  oxide  of  iron, 
or  magnesia,  &c.  The  different  kinds  of  clay  are  most  abun¬ 
dantly  spread  over  the  globe,  forming-  in  many  situations  entire 
mountains,  in  other  places  existing  in  vast  beds,  and  elsewhere 
lying  among  other  mineral  substances  disposed  in  strata.  It 
has  been  generally  held  that  clay  results  from  the  slow  decom¬ 
position  of  silicious  and  aluminous  rocks,  which  being  acted  on 
by  water  filtrating  through  them,  their  constituent  parts  have, 
in  the  course  of  ages,  been  separated  ;  the  lighter  and  finer  por¬ 
tions  remaining  united  at  the  top,  while  the  grosser  but  less 
tenacious  parts  have  been  resolved  into  sandy  deposits. 

Silica,  or  pure  flint,  which  forms  the  second  material  in  the 
composition  of  pottery,  has  been  considered  as  a  primitive  earth. 
It  is  of  very  common  occurrence  in  most  parts  of  the  world,  in 


30 


PORCELAIN  MANUFACTURE. 


CHAP.  II. 


primitive  mountains.  It  is  frequently  found  in  great  abundance 
embedded  in  chalk.  In  Scotland  and  Ireland  it  occurs  in  second¬ 
ary  limestone.  Flint  abounds  in  alluvial  districts  in  the  form 
of  gravel :  an  inexhaustible  supply  of  excellent  quality  might 
be  collected  on  some  parts  of  the  sea-coast  of  England,  and 
particularly  at  and  near  Brighton,  where  there  is  enough  of 
this  material,  known  under  the  name  of  shingle,  to  serve  the 
whole  manufacturing  wants  of  England  for  ages  to  come,  while 
its  removal  would  be  attended  with  advantage  to  the  place 
whence  it  should  be  taken.  Flint  is  silica  in  a  state  nearly  ap¬ 
proaching  to  purity,  its  constituents  being 

Silica . 98. 

Lime . 0.50 

Alumina  ....  0.25 
Oxide  of  iron  .  0.25 
Loss . 1. 


100. 


It  is  usually  gray,  with  occasional  striped  delineations  occur¬ 
ring  in  its  substance.  It  it  obtained  generally  in  rolled  pieces, 
but  often  occurs  in  irregular  shapes.  It  has  internally  a  glim¬ 
mering  lustre ;  its  fracture  is  conchoidal,  and  its  fragments  are 
sharp-edged.  It  is  translucent.  When  two  pieces  are  rubbed 
together  in  the  dark,  they  emit  a  phosphorescent  light,  and 
give  off  a  peculiar  smell.  We  are  unable  to  dissolve  silex  in 
water.  This  process  is,  however,  constantly  performed  by  na¬ 
ture.  The  investigations  of  Klaproth  enabled  him  to  detect 
25  grains  of  silex  in  1000  ounces  of  the  principal  mineral 
spring  at  Carlsbad,  in  Bohemia ;  and  the  celebrated  boiling 
fountain  at  Rykum,  in  Iceland,  deposits  so  considerable  a  quan¬ 
tity  of  silicious  earth,  that  a  solid  cup  has  been  formed  around 
it,  rising  to  a  considerable  height.  This  solution  of  silica  is 
probably  owing,  in  both  these  cases,  to  the  solvent  power  of  soda  ; 
which  is  also  present  in  the  water.  The  water  from  the  spring 
at  Rykum  used  formerly  to  be  projected  into  the  air  to  the  per¬ 
pendicular  height  of  60  or  70  feet ;  but  the  overthrow  of  a 
mass  of  rock  having  since  partially  covered  its  orifice,  the 
stream  spouts  out  laterally  to  a  distance  of  50  or  60  feet.  The 
heat  of  the  liquid,  after  it  has  reached  the  surface,  is  sufficient 
to  raise  the  thermometer  to  the  boiling  point  of  water;  and 
there  is  little  doubt  that  the  fluid  must  have  parted  with  some 
portion  of  its  heat  on  emerging  into  the  atmosphere.  The  ca¬ 
pability  of  water,  in  its  dense  or  liquid  state,  to  assume,  under 
these  circumstances,  a  higher  degree  of  heat  than  that  at  which 
it  boils  under  ordinary  atmospheric  pressure,  may  be  partly  at- 


CHAP.  II.  KIA'DS  OF  CLAY  USED  IX  POTTEKIES.  37 

tributable  to  the  depth  from  which  it  is  brought,  influenced  by 
the  same  law  that  occasions  fluids  to  boil  at  lower  temperatures 
on  the  tops  of  high  mountains.  Silica  is  also  found  existing  in 
solution  in  the  Bath  waters. 

The  best  flints  are  of  a  dark  gray  color,  approaching  to  black, 
and  having  a  considerable  degree  of  transparency.  Those 
which  exhibit  brown  or  yellow  spots  on  their  interior  surfaces 
should  be  rejected,  on  account  of  the  ferruginous  particles 
which  they  contain,  and  which  would  occasion  blemishes  in  the 
ware.  Those  larger  masses  of  flint  are  always  most  preferred 
by  the  potter,  which,  being  dark  and  clear  within,  are  covered 
with  a  white  crust  externally.  The  rolled  pieces  which  are 
taken  from  chalk  pits  are  mostly  of  this  description. 

De  Saussure  asserts  that  pure  silex  may  be  fused  at  a  heat 
equal  to  4043  degrees  of  Wedgwood’s  pyrometer;  a  degree  so 
far  beyond  any  that  has  yet  been  observed,  that  one  is  at  a  loss 
to  know  upon  what  data  the  assertion  is  founded. 

The  clay  principally  used  in  the  potteries  of  Staffordshire  is 
brought  to  them  from  Dorsetshire  and  Devonshire.  These 
earths  are  both  of  excellent  working  quality,  and,  being  free 
from  any  impregnation  of  iron,  are  valuable  for  the  great  white¬ 
ness  which  they  exhibit  when  burnt.  The  Dorsetshire  clay  is 
brought  from  the  Isle  of  Purbeck.  It  is  of  two  kinds,  distinguish¬ 
ed  as  brown  clay  and  blue  clay :  that  from  Devonshire  comes 
from  the  southern  part  of  the  county,  and  is  also  of  two  distinct 
qualities,  which  are  known  as  black  clay  and  cracking  clay. 
The  clay  from  Dorsetshire  is  considered  preferable  to  that  from 
Devonshire  for  the  potter’s  use ;  so  that  it  commands  a  price 
in  the  potteries  equal  to  one  eighth  more  than  the  latter. 

The  good  qualities  of  brown  clay  are,  that  it  burns  of  an 
excellent  white,  and  is  not  liable  to  crack  during  the  process 
of  burning.  On  the  other  hand,  it  is  subject  to  the  considera¬ 
ble  imperfection  of  crazing, — an  evil  which  induces  some  man¬ 
ufacturers  to  discard  it  altogether  from  their  works.  Crazing 
is  a  technical  phrase,  used  to  denote  the  cracking  of  the  glaze, 
which  is  believed  to  arise  from  the  imperfect  manner  in  which 
this  is  capable  of  uniting  itself  with  the  clay  composing  the 
body  of  the  vessel.  This  defect  of  crazing  is  not,  however,  al¬ 
ways  referable  to  the  cause  here  assigned,  but  may  be  owing 
equally  to  the  faulty  nature  of  the  glaze,  which  may  not  be  ca¬ 
pable  of  perfect  fusion  in  the  heat  of  the  kiln ;  or  it  may  result 
from  the  error  of  the  workmen  in  withdrawing  the  wares  from 
the  kiln  at  too  early  a  period,  and  before  they  are  properly 
cooled ;  the  glaze,  which  is  in  fact  glass,  requiring  great  care¬ 
fulness  in  this  respect  for  its  proper  annealing,  and  being,  with- 


38 


PORCELAIN  MANUFACTURE. 


CHAT.  II. 


out  it,  very  liable  to  crack  with  every  material  variation  of 
temperature  to  which  it  may  be  suddenly  exposed. 

Blue  clay  combines  the  greatest  number  of  good  qualities, 
and  is  the  most  generally  esteemed,  of  all  the  four  descriptions 
here  mentioned.  It  burns  exceedingly  white,  forms  a  very  solid 
quality  of  ware,  and  is  capable  of  being  advantageously  com¬ 
bined  with  a  greater  quantity  of  silicious  earth,  or  flint,  than 
any  of  the  other  kinds ;  a  quality  which  is  desirable,  because 
the  greater  the  proportion  of  silica  that  is  used,  the  whiter  will 
prove  the  ware  :  the  limit  to  the  use  of  flint  being  the  inability 
of  the  clay  to  bear  it  in  combination  beyond  a  certain  propor¬ 
tion  without  cracking.  Both  these  descriptions  of  clay  are 
much  used  as  ingredients  in  the  manufacture  of  porcelain. 

Black  clay  owes  its  distinctive  color  to  the  quantity  of  coaly 
or  bituminous  matter  which  it  holds  in  combination,  but  which 
is  entirely  consumed  and  dissipated  when  the  clay  is  submitted 
to  the  heat  of  the  oven,  leaving  the  articles  of  which  it  is  com¬ 
posed  of  a  very  good  white  ;  and  which  is,  indeed,  found  to  be 
the  more  perfect  in  proportion  as  the  clay  has  originally  been 
blacker.  Cracking  clay  has  acquired  its  name  from  an  evil 
property  of  occasioning  the  ware  to  crack  while  undergoing 
the  first  application  of  fire.  To  compensate  in  some  degree  for 
this  evil,  the  goods  in  which  it  is  employed  prove  of  an  ex¬ 
treme  whiteness.  Much  judgment  and  experience  must  be 
brought  to  the  employment  of  this  clay,  that  its  tendency  to 
cracking  may  be  as  much  as  possible  corrected  by  a  propor¬ 
tionate  admixture.  If  clay  of  any  description  were  dried  with¬ 
out  the  addition  of  any  other  body,  after  being  made  sufficiently 
plastic  to  be  modelled  on  the  potter’s  wheel,  it  must  inevitably 
crack,  as  the  evaporation  of  its  water  will  occasion  it  to  shrink 
in  the  proportion  of  one  part  in  twelve  during  the  drying. 

Another  description  of  clay,  much  prized  for  the  manufacture 
of  finer  kinds  of  earthenware  and  porcelain,  was  found  in  Corn¬ 
wall  by  Mr.  Cookworthy,  as  already  mentioned,  and  is  com¬ 
monly  denominated  China  clay.  This  is  very  white  and  unc¬ 
tuous  to  the  touch,  and  is  obviously  formed  by  the  gradual  dis¬ 
integration  of  the  felspar  of  granite.  There  are  found  in  Corn¬ 
wall  large  mountains  of  this  mineral,  some  of  which  are  thus 
partially  decomposed  ;  this  China  clay  proves,  on  examination, 
to  be  identical  with  the  kao-lin  of  the  Chinese.  It  was  found 
by  Mr.  Gerhard  in  the  course  of  some  experiments  upon  granite 
(which  is  a  compound  of  quartz,  felspar,  and  mica,)  that  the 
felspar  was  melted  into  a  transparent  glass,  that  the  mica  was 
found  lying  under  it  in  the  form  of  a  black  slag,  while  the 
quartz  remained  unaltered. 

The  Ciiina  clay  of  Cornwall  is  prepared  by  the  clay  mer- 


CHAP.  II.  KINDS  OF  CLAY  USED  IN  POTTERIES.  39 

chants  on  the  spot  where  it  is  found.  The  stone  is  broken  up 
into  pieces  of  a  small  size,  and  then  cast  into  a  running  stream : 
there  the  light  argillaceous  parts  are  washed  oif  and  held  sus¬ 
pended  in  the  water,  while  the  more  ponderous  mica  and  quartz 
remain  at  the  bottom  of  the  stream.  At  the  end  of  the  rivulet 
the  water  is  stopped  by  a  dam,  and  the  pure  clay  gradually  sub¬ 
sides.  When  this  deposit  is  completed,  the  clear  water  is  drawn 
oftj  and  the  solid  matter  dug  out  in  square  blocks,  which  are 
placed  on  shelves,  and  exposed  to  a  continued  current  of  air 
until  sufficiently  dry  to  be  packed  in  casks  for  shipment.  This 
clay,  which  is  then  in  the  state  of  a  fine  powder,  is  very 
smooth,  and  of  an  extreme  whiteness.  Mr.  YVedgwood  found 
by  analysis  that  it  contains  sixty  parts  of  alumina  and  twenty 
parts  of  silica.  The  manufacturers  are  required  to  pay  a  much 
higher  price  for  this  than  for  any  other  of  our  native  earths, 
but  for  some  finer  purposes  it  is  altogether  indispensable. 

A  portion  of  undecomposed  Cornish  felspar  is  often  added  to 
the  clay,  on  account  of  its  fusibility  and  tenaciousness,  by  which 
it  binds,  as  it  were,  the  whole  ingredients  more  closely  together. 
The  fusible  quality  of  felspar  is  owing  to  the  presence  of  about 
an  eighth  part  of  potass.  If  this  alkaline  substance  be  sepa¬ 
rated  by  decomposition,  as  is  the  case  with  the  China  clay  above 
described,  the  fusibility  no  longer  exists,  and  the  body  remains 
unaltered  in  the  greatest  heat  of  a  porcelain  furnace.  The  use 
of  this  material  has  of  late  been  very  much  increased  in  our 
porcelain  works.  It  is  a  curious  and  very  useful  fact,  that  al¬ 
though  neither  clay,  flint,  nor  lime  can  be  separately  melted, 
yet  when  mixed  together  in  due  proportions,  the  mass  is  fused 
without  difficulty,  the  one  mineral  acting  as  a  flux  to  the  other. 

Steatite,  or  soapstone,  has  of  late  years  been  very  much  em¬ 
ployed  in  the  composition  of  porcelain.  When  present,  in  even 
a  small  proportion,  it  limits  the  contraction  of  the  ware  in  the 
furnace.  Steatite  is  a  sub-species  of  mica,  which  is  found 
abundantly  in  Cornwall,  and  is  met  with  also  in  the  island  of 
Anglesea.  The  mineral  which  forms  the  porcelain  earth  of 
Baudissero,  was  long  considered  to  be  a  superior  kind  of  clay, 
until  it  was  discovered  by  M.  Geobert  that  it  contains  not  a  par¬ 
ticle  of  alumina  in  its  composition.  This  chemist,  on  endeavor¬ 
ing  to  convert  the  substance  into  alum,  found,  to  his  great  sur¬ 
prise,  that  he  obtained  only  crystals  of  sulphate  of  magnesia 
(Epsom  salts).  Proceeding  thence  to  analyze  it  carefully,  he 
ascertained  its  composition  to  be,  magnesia  68,  carbonic  acid 
12,  silica  156,  sulphate  of  lime  1-6,  water  2*8.  The  soapstone 
of  Cornwall  differs  from  this  substance,  yielding  on  analysis, 
magnesia  44,  silica  44,  alumina  2,  iron  7-3,  magnesia  15, 
chrome  1-2.  It  also  contains  traces  of  lime  and  muriatic  acid. 


40 


PORCELAIN  MANUFACTURE. 


CHAP.  II. 


In  a  published  letter  addressed  by  M.  Proust  to  M.  Vauque- 
lin  from  Madrid,  mention  is  made  of  a  beautiful  kind  of  porce¬ 
lain  produced  in  that  city,  and  which  is  described  to  be  of  a 
texture  even  harder  than  the  porcelain  of  France.  Instead  of 
employing  the  kao-lin,  the  body  of  the  ware  is  made  with  spu- 
mi  maris,  a  species  of  pot-stone  found  in  the  neighborhood  of 
Madrid,  and  the  glaze  is  composed  of  felspar  brought  from  Gal- 
licia.  The  pot-stone  when  taken  from  the  quarry  is  sufficiently 
soft  to  admit  of  its  being  cut  with  a  knife  like  soap.  Besides 
magnesia,  silex,  and  some  particles  of  argil  and  lime,  it  con¬ 
tains  a  portion  of  potass,  the  presence  of  which,  in  the  com¬ 
petent  opinion  of  M.  Proust,  contributes  not  a  little  to  the  su¬ 
perior  quality  of  the  manufacture. 


CHAP.  III. 

ON  THE  PREPARATION  OF  MATERIALS. 

Dilation  of  Clay. — Chemical  Examination  of  Water  necessary. — Rain  Wa¬ 
ter. — Carefulness  of  German  Manufacturers. — Blunging. — Machinery. — 
Preparing  Flints.  —  Burning.  —  Breaking.  —  Grinding.  —  Dry  Grinding. — 
Brindley’s  Improved  Mill  —Chert. — Care  require!  in  selecting  Grinding 
Stones.— Dilution  of  Flint-Powder. — Proper  Consistence  of  Dilution. — Ad¬ 
mixture  in  due  Proportions. — Affinity  of  Alumina  for  Silica. — Slip. — 
Slip-Kiln. — Method  of  evaporating  superfluous  Moisture. — Working  the 
Paste. — Time  necessary  for  tempering  it  — Proportions  wherein  Clay  and 
Flint  are  united.  —  Difficulty  of  ascertaining  this. — Slapping.  —  French 
Manufacturers.— Proportions  of  Ingredients  used  by  them. — Kao-Lin. — 
Flint. — Gypsum. — Broken  Porcelain. — Calcined  Bones. — Tender  Porcelain. 
— Its  Composition. — Porcelain  Earth  used  in  Berlin. — French  Potters  buy 
their  Materials  ready  mixed. — Advances  on  this  Plan. — Ineligible  in  Eng¬ 
land. 

In  preparing  the  clay,  the  first  operation  of  the  pottery  is 
that  of  mixing  it  with  water  to  the  consistence  of  cream.  It 
is  well  known,  that  water  collected  from  springs,  and  from 
many  streams,  contains  various  foreign  matters,  some  of  which 
would  be  injurious  to  the  composition  of  porcelain.  It  is  there¬ 
fore  necessary  to  examine  chemically  the  properties  of  water 
before  it  is  employed  for  this  purpose,  in  order  to  make  choice 
of  that  which  is  purest ;  and  to  correct,  by  some  of  the  well- 
known  means,  any  bad  qualities  that  may  be  present.  The 
French  manufacturers  are  accustomed  to  employ  only  rain 
water,  whose  near  approach  to  purity  fits  it  for  the  object  In 
Germany,  still  more  precise  in  his  operations,  the  manufacturer 
prepares  his  materials  only  twice  in  the  year,  at  the  vernal  and 
autumnal  equinoxes;  persuading  himself  that  at  these  seasons 
there  is  some  peculiarity  in  the  rain  which  better  qualifies  it  for 


CHAP.  III.  PREPARATION  OF  MATERIALS.  41 

the  purpose  of  his  manufacture.  Although  the  grounds  for  this 
nicety  are  not  apparent,  it  would  savor  of  presumption  to  at¬ 
tribute  the  practice  entirely  to  prejudice.  The  observations  of 
men  practically  engaged  in  manual  or  chemical  operations  have 
frequently  led  to  improvements  in  processes,  long  before  the 
reasons  whereon  these  should  have  been  founded  have  been  re¬ 
vealed  by  scientific  researches. 

The  mixing  of  the  clay,  which  is  called  blunging ,  is  effected 
in  a  trough  five  feet  long,  three  feet  wide,  and  two  and  a  half 
feet  deep.  In  order  fully  to  break  down  the  clay,  and  incor¬ 
porate  it  with  the  water,  a  long  wooden  instrument,  formed 
with  a  blade  at  one  end  and  a  cross  handle  at  the  other,  is 
moved  violently  about  in  the  trough  in  all  directions,  so  that 
this  becomes  an  operation  of  great  labor.  In  large  establish¬ 
ments,  where  machinery  is  adopted  for  the  abridgement  of  la¬ 
bor,  the  blunging  is  thus  effected : — The  clay  is  thrown  into  a 
cast  iron  cylinder,  four  feet  deep,  and  twenty  inches  in  diam¬ 
eter.  Through  the  centre  of  this  cylinder  runs  an  upright 
•  shaft,  furnished  with  knives  placed  as  radii  at  right  angles  to 
the  shaft,  but  so  arranged  upon  it  that  their  flat  sides  are  in 
the  plane  of  a  spiral  thread,  so  that  by  the  revolutions  of  the 
shaft,  the  knives  perform  the  double  office  of  cutting  what¬ 
ever  stands  in  their  way,  and  of  forcing  downwards  the  con¬ 
tents  of  the  cylinder  in  the  manner  of  a  screw.  Another  set 
of  knives  is  inserted  in  the  interior  surface  of  the  cylinder, 
and  these  extend  to  the  shaft  in  the  centre,  parallel  to,  and 
corresponding  with,  the  revolving  knives:  thus  the  two  sets, 
the  one  active  and  the  other  passive,  have  the  effect  of  shears 
in  cutting  the  clay  into  small  pieces ;  while  this,  in  its  reduced 
state,  is  at  the  same  time  forced  through  an  aperture  at  the 
bottom  of  the  cylinder,  and  transferred  to  a  vat  for  the  purpose 
of  being  mixed  with  water ;  a  process  which  this  previous  di¬ 
viding  of  the  clay  is  found  materially  to  facilitate. 

The  vat  where  this  mixture  is  performed  is  likewise  of  a 
cylindric  form,  its  diameter  being  equal  to  four  times  its  depth. 
In  the  centre  of  this  vat,  also,  a  perpendicular  shaft  is  inserted, 
furnished  with  cross  arms  or  radii,  one  below  the  other.  These 
cross  arms  are  connected  by  upright  staves,  giving  the  appear¬ 
ance  of  two  opposite  gates  hung  upon  the  central  shaft.  These 
revolve  within  the  cylinder;  and  as  they  are  partially  immersed 
in  the  pulp,  the  constant  agitation  mixes  all  the  finer  particles 
of  clay  with  the  water,  while  stony  particles  of  greater  magni¬ 
tude  fall  to  and  remain  at  the  bottom.  The  pulp,  now  mixed  to 
the  consistence  of  cream,  is  passed  off  from  the  vat  through  a 
series  of  sieves  of  increasing  degrees  of  fineness,  which  are 
worked  to  and  fro  by  machinery  ;  thus  a  separation  is  effected 

D  2 


42 


PORCELAIN  MANUFACTURE. 


CHAP.  III. 


between  the  grosser  parts  and  that  portion  which  is  fitted  to 
enter  into  the  composition  of  the  ware. 

The  next  process  is  that  of  preparing  the  flints.  These  are 
first  burnt  in  a  kiln  constructed  for  the  purpose,  and  which 
very  much  resembles  an  ordinary  lime-kiln,  being  of  a  conical 
shape,  and  about  nine  feet  deep.  While  the  flints  are  yet  red- 
hot,  they  are  removed  from  the  kiln,  and  in  that  state  are 
thrown  into  cold  water  ;  by  means  of  which  their  attraction  of 
aggregation  is  lessened,  so  as  to  facilitate  greatly  the  subse¬ 
quent  operation  of  grinding :  they  are  next  broken,  either  by 
manual  labor,  or  by  machinery.  In  the  latter  case  they  are 
placed  upon  a  strong  iron  grating,  and  there  struck  by  ham¬ 
mers,  until  sufficiently  reduced  in  size  to  fall  through  the  gra¬ 
ting  to  a  receiver,  whence  they  are  conveyed  to  the  flint  mill. 

In  order  to  expedite  the  process,  and  at  the  same  time  to 
grind  the  flints  finer,  a  quantity  of  water  is  thrown  with  them 
into  the  mill.  Another  good  attending  the  presence  of  water 
in  this  grinding  operation,  is  the  preservation  of  the  health  of 
the  workmen.  Before  the  adoption  of  this  method,  the  atmo¬ 
sphere  of  the  room  became  charged  with  the  finer  particles  of 
flint,  which,  adhering  to  the  lungs,  frequently  occasioned  dis¬ 
tressing  and  sometimes  fatal  diseases  to  the  workmen.  This 
great  improvement  was  effected  by  the  illustrious  Brindley, 
who  likewise  invented  the  mill  now  used  in  the  process.  This 
is  a  large  circular  vat,  about  thirty  inches  deep,  having  a  cen¬ 
tral  step  fixed  in  the  bottom  to  carry  the  axis  of  a  vertical 
shaft.  The  moving  power  is  applied  to  this  shaft  by  a  crown 
cog  wheel  placed  on  the  top.  At  the  lower  part  of  the  shaft, 
and  at  right  angles  to  it,  are  fixed  four  arms,  upon  which  the 
grinding  stones  are  fixed  ;  large  blocks  of  stone  of  the  same 
kind  being  likewise  placed  in  the  vat.  These  stones  are  a  very 
hard  silicious  mineral,  called  chert,  which  is  found  in  abun¬ 
dance  in  the  neighborhood  of  Bakewell,  in  Derbyshire.  The 
broken  flints  being  then  introduced  and  completely  covered 
with  water,  the  axis  is  made  to  revolve  with  great  velocity, 
when  the  calcined  flints  are  speedily  reduced  to  an  impalpable 
powder. 

The  nature  of  the  grinding  stones  used  in  these  flint  mills  is 
of  considerable  importance ;  for  should  they  contain  any  calca¬ 
reous  carbonate,  they  will  be  abraded  ;  some  part  of  their  sub¬ 
stance  will  mix  with  the  flint,  and  consequently  with  the  body 
of  the  wares,  and  thus  occasion  very  serious  injury  to  the  man¬ 
ufacturer.  Some  years  ago,  a  very  heavy  loss  was  sustained  by 
some  potters,  who  had  purchased  flints  ground  in  a  mill  the 
stones  of  which  contained  carbonate  of  lime. 

When  the  flints  are  thus  sufficiently  ground,  the  semi-fluid 


CHAP.  in.  PREPARATION  OF  MATERIALS.  43 

is  transferred  to  another  vat,  also  constructed  with  an  upright 
shaft  furnished  with  arms  or  vanes  for  the  purpose  of  agitation  ; 
and  a  considerable  quantity  of  water  being  added,  the  moving 
power  is  applied,  and  the  whole  violently  agitated.  The  pr<> 
cess  occasions  the  grosser  and  weightier  particles  to  take  their 
place  at  the  bottom,  while  the  finer  portion  remains  in  suspen¬ 
sion  above ;  and  in  this  state  is  passed  for  subsidence  to  a  reser¬ 
voir,  whence  in  due  time  the  supernatant  water  is  drawn  off 
through  apertures  provided  for  the  purpose. 

The  dilution  of  clay  is  held  to  be  of  the  proper  consistence 
for  mixing,  when  a  quantity  that  will  fill  a  pint  measure 
weighs  twenty-four  ounces ;  and  that  of  the  flints  is  equally 
considered  suitable  for  use,  when  the  same  bulk  is  brought  to 
weigh  thirty-two  ounces.  It  is  by  their  specific  gravities,  that 
is,  by  the  comparative  densities  of  these  dilutions,  as  indicated 
by  weighing  an  equal  bulk  of  each,  that  the  manufacturer  is 
enabled  to  ascertain  the  real  proportions  of  the  materials,  and 
to  combine  them  in  the  degrees  which  his  experience  leads  him 
to  employ  for  the  composition  of  various  kinds  of  pottery  ;  and 
too  much  nicety  can  hardly  be  given  to  this  important  part  of 
his  labors. 

The  dilutions  of  clay  and  flint  being  brought  together  in 
suitable  proportions,  and  intimately  united  by  agitation,  the 
mixture  is  passed,  while  in  a  state  of  semi-fluidity, “through  dif¬ 
ferent  sieves,  in  order  to  separate  any  remaining  impuritfes,  to¬ 
gether  with  such  portions  as  have  not  been  sufficiently  ground. 
By  these  means  the  mass  presents  the  utmost  uniformity  and 
smoothness  throughout.  The  affinity  which  alumina  has  for 
silica,  under  all  circumstances,  is  so  great,  that  they  will  unite 
ewen  in  the  humid  way,  forming  a  kind  of  mortar;  and  when 
this  becomes  hardened  by  time,  it  is  thereafter  incapable  of  de¬ 
composition  by  the  action  of  the  atmosphere. 

This  fluid  mixture  ot  clay  and  flint  is  called  slip,  and,  after 
passing  through  the  sieves,  is  pumped  to  the  slip  kiln.  This  is 
a  kind  of  trough  formed  of  fire-bricks  ;  its  size  varies  according 
to  the  extent  of  the  manufactory,  being  of  the  length  of  forty 
to  sixty  feet,  from  four  to  six  feet  wide,  and  about  twelve  to 
eighteen  inches  deep.  Flues  from  fire-places  pass  under  the 
whole  extent  of  the  troughs,  in  which  the  fluid  is  made  to  boil, 
and  the  process  of  evaporation  is  slowly  conducted,  so  as  to 
produce  an  uniform  consistency  throughout  the  mass.  This 
evaporation  must  be  very  carefully  attended,  and  the  mass  fre¬ 
quently  stirred  and  turned  over,  otherwise,  from  the  imperfect 
manner  in  which  it  conducts  heat,  the  portion  in  contact  with 
the  bricks  would  become  improperly  hardened,  while  the  re¬ 
mainder  would  continue  fluid ;  in  addition  to  which,  flint  being 


44 


PORCELAIN  MANUFACTURE. 


CHAP.  III. 


specifically  heavier  than  clay,  the  former  would  in  the  first  part 
of  the  process,  and  while  the  slip  is  yet  fluid,  have  a  natural 
tendency  to  subside  to  the  bottom,  and  thus  render  the  com¬ 
position  of  the  mass  unequal. 

The  evaporation  is  never  carried  beyond  a  certain  point  in 
the  kiln ;  for  should  the  mass  become  too  dry,  it  would  be  im¬ 
possible  to  knead  it  properly,  or  to  mould  it  on  the  wheel  into 
any  of  the  forms  which  it  is  desired  to  create.  The  place 
where  this  evaporation  is  performed  is  called  the  slip-house. 

When  the  clay  or  paste  is  removed  from  the  slip-kiln  it  con¬ 
tains  a  great  number  of  air-bubbles,  and  must  be  well  incorpo¬ 
rated  together  or  tempered  by  working  or  beating  it  with 
wooden  mallets.  It  is  next  cut  with  a  kind  of  spade  into  small 
pieces,  which  are  thrown  upon  the  mass  with  all  the  strength 
of  the  workmen,  and  these  operations  are  persisted  in  until  it 
is  supposed  that  their  further  continuance  would  not  bring  the 
whole  to  a  more  complete  state  of  consistence. 

The  mixture,  when  brought  to  this  state,  should  be  suffered 
to  remain  in  a  mass  for  a  considerable  time  before  it  is  used ; 
the  material  by  this  course  becomes  much  more  intimately 
united  than  can  ever  be  effected  by  mechanical  means.  It  is 
to  be  feared  that,  although  the  English  potters  are  fully  aware 
of  this  fact,  they  yet  fail  to  adopt  so  eligible  a  practice,  which, 
as  it  calls  for  the  employment  of  greater  space,  time,  and  capi¬ 
tal,  is  neglected  for  other  advantages,  which,  if  not  so  great  in 
an  extended  point  of  view,  are  certainly  more  immediate. 

It  is  not  possible  to  state  the  precise  proportions  wherein  the 
clay  and  flint  are  brought  together  in  our  English  potteries. 
Each  manufacturer  has  in  this  respect  his  own  practice,  which, 
esteeming  it  as  the  best,  he  endeavors  to  keep  profoundly  se¬ 
cret  ;  and,  besides,  the  proportions  necessarily  vary  with  the 
quality  and  properties  which  it  is  desired  to  give  to  the  manu¬ 
facture.  Yauquelin  informs  us  that  silex  forms  at  least  two 
thirds  of  all  kinds  of  pottery ;  alumine  from  one  fifth  to  one 
third;  lime  from  1 -500th  to  l-2000th  part;  and  iron  from  the 
smallest  conceivable  quantity  up  to  twelve  and  sometimes  even 
fifteen  per  cent.  The  presence  of  the  two  latter  bodies  is  ac¬ 
cidental,  arising  from  the  natural  composition  of  the  materials, 
and  in  particular  the  oxide  of  iron,  when  present  in  any  sen¬ 
sible  degree,  renders  the  clay  unfit  for  all  purposes,  except  that 
of  forming  the  common  red  ware. 

Parkes,  whose  practical  essay  on  the  making  of  earthenware 
and  porcelain  is  founded  on  his  own  personal  observations, 
made  during  a  residence  of  some  years’  continuance  at  the  seat 
of  manufacture,  is  yet  so  little  able  to  be  precise  upon  the  sub- 


CHAP.  III.  PREPARATION  OF  MATERIALS. 


45 


ject  of  proportions,  that  he  tells  us  flint  forms  a  fourth,  a  fifth, 
or  a  sixth  part  by  weight  of  the  prepared  paste. 

,JTet-POrtr  0f  thf  china-clay  of  Cornwall  enters  into  the 
composition  of  every  better  kind  of  earthenware,  except  only 

thp  m'C°i°md  S°rt;  ThiS  ln-redient  is  sometimes  added  to 
the  mass,  and  blunged  with  it,  and  at  other  times  is  blunoed 

eparately  and  mixed  in  the  required  proportion  with  the  slip. 

he  clay  or  paste,  when  taken  for  use,  undergoes  the  pro- 
cess  of  slapping.  This  labor  is  assigned  to  a  man  of  con- 

who  Proceeds  by  placing  a  lump  weighing 
n  fifty  to  sixty  pounds  upon  a  convenient  slab  or  bench, 
ihe  mass  is  then  cut  through  with  a  thin  brass  wire,  one  end 
of  which  is  held  in  either  hand,  while  the  part  between  is 
forced  through  the  clay,  which  separates  as  easily  as  if  it  were 
cut  with  a  knife;  then  taking  up  with  both  hands  the  piece 
thus  separated,  and  exerting  his  utmost  strength,  he  hurls  it  on 
_  ?  rest  of  the  mass ;  and  this  operation  is  repeated  until  the 
ole  lump  exhibits  a  perfectly  smooth  and  close  appearance 
herever  it  is  cut.  feo  complete  is  the  incorporation  of  the 
whole  mass  by  this  means,  that  if,  at  the  commencement  of  the 
process,  two  pieces  of  clay  of  different  colors  are  taken,  the 
ump,  at  its  completion,  will  be  of  one  uniform  hue,  intermedi¬ 
ate  to  the  two  original  colors.  This  laborious  operation  is  one 
ot  ^e  very  first  necessity,  in  order  completely  to  expel  every 
air-bubble  however  minute,  remaining  in  the  clay,  and  wdnch 
could  not  be  so  thoroughly  driven  out  by  its  previous  beating  in 
the  larger  mass  when  taken  from  the  slip-kiln.  If  the  air 
were  not  thus  thoroughly  expelled,  it  would  become  so  much 
ranfied  and  expanded  in  the  oven,  that  it  would  force  out  a 
goods^6  °r  J^Se  anc^  ky  blistering,  spoil  or  much  injure  the 

Some  of  the  more  considerable  among  the  potters,  who  em¬ 
ploy  steam  power  for  blunging  the  clay  and  grinding  the  flints, 
perform  this  operation  of  slapping  by  the  same  agency,  savin°- 
thereby  both  time  and  labor.  In  this  case  the  expulsion  of  the 
iir  is  effected  by  mechanical  pressure,  and  the  office  is  per- 
■ormed  with  perhaps  as  much  efficiency  as  by  hand. 

,  saving  undergone  all  these  preparations,  the  clay  is  now  fit 
or  being  shaped  upon  the  wheel  or  fashioned  by  the  aid  of 
noulds  into  all  the  diversified  forms  which  fancy  may  desire. 
lhis„  branch  of  the  art  is  divided  into  three  different  depart- 
:  nen  s— throwing,  pressing,  and  casting— either  of  which  is 
ismI  according  to  the  form  of  the  article  manufactured. 

ie  manufacturers  of  porcelain  in  France  do  not  use  so 
such  secrecy  as  is  preserved  in  our  own  potteries,  with  re- 
pec  either  to  the  materials  whereof  their  w?are  is  compound- 


46 


PORCELAIN  MANUFACTURE. 


CHAP.  III. 


ed,  or  to  the  proportions  wherein  these  are  employed.  The 
clay  which  forms  five  parts  in  six  of  the  whole  mass,  is  the 
porcelain  earth  already  mentioned  as  being  identical  with  the 
kao-lin  of  China ;  to  this  are  added  in  certain  proportions  flint 
and  gypsum  (plaster  of  Paris),  both  calcined  and  ground ;  and 
fragments  of  broken  porcelain,  which  must  be  white,  also 
ground  to  a  fine  powder.  One  rule  for  forming  this  composi¬ 
tion  assigns  nine  parts  each  of  flint  and  broken  porcelain,  and 
four  parts  of  calcined  gypsum,  to  each  one  hundred  parts  of 
porcelain  clay.  Another  authority  recommends  five  parts  of 
gypsum  and  only  eight  parts  of  ground  porcelain ;  while  the 
flint  and  clay  are  used  in  the  same  proportions  as  in  the  first 
rule.  If  at  any  time  the  manufactory  should  not  afford  broken 
porcelain  for  the  purpose,  it  is  recommended  that  pieces  be 
compounded,  about  a  quarter  of  an  inch  thick,  of  the  other 
three  ingredients,  wherein  the  proportions  of  gypsum  and  flint 
are  augmented ;  and  these  pieces,  having  been  previously  con¬ 
verted  into  porcelain  by  baking,  are  to  be  ground  and  mixed  in 
the  above-mentioned  proportions  with  the  other  ingredients. 

It  has  of  late  years  been  the  practice  of  some  English  manu¬ 
facturers  to  use  a  considerable  proportion  of  calcined  bones,  to¬ 
gether  with  a  small  quantity  of  gypsum,  in  combination  with 
china-clay,  flint,  Cornish  stone  and  enamel.  By  this  means 
porcelain  of  a  brilliant  and  very  transparent  white  is  produced, 
which,  however,  is  deficient  in  density,  and  very  liable  to  crack 
on  the  application  of  hot  liquids. 

Several  among  the  chemists  and  scientific  manufacturers  of 
porcelain  in  France  have  given  recipes  for  the  composition  of 
tender  porcelain,  although  this  description  of  ware  is  no  longer 
made  in  that  country. 

This  kind  of  porcelain  will  support,  without  softening,  a 
greater  degree  of  heat  than  suffices  to  melt  glass.  It  is  semi¬ 
transparent,  has  a  vitreous  fracture,  and  returns  a  clear  sound 
when  struck  by  a  hard  body.  It  is  harder  but  not  so  brittle  as 
glass,  and  bears,  without  injury,  sudden  and  very  considerable 
alterations  of  temperature. 

M.  Brongniart  recommends  a  mixture  of  one  part  of  pure 
white  clay,  with  three  parts  of  a  frit  compounded  of  nitre, 
soda,  alum  and  selenite  (sparry  gypsum),  together  with  a  large 
proportion  of  ferruginous  sand  and  a  little  common  salt.  The 
ingredients  of  this  frit  are  to  be  calcined  together,  and  the 
whole  intimately  kneaded ;  when  cold,  the  compound  is  to  be 
reduced  to  powder,  and  in  that  state  mixed  with  the  clay. 

This  paste  is  not  so  cohesive  or  viscous  as  that  which  forms 
hard  porcelain,  and  greater  carefulness  is,  therefore,  called  for 
in  fashioning  vessels  with  it.  Lime  and  selenite,  or  any  similar 


CHAP.  III.  PREPARATION  OF  MATERIALS.  47 

earths  which,  if  fused  by  themselves,  produce  a  transparent 
and  colorless  glass,  may  answer  the  same  purpose  as  the  frit 
just  mentioned.  In  making  choice,  however,  of  the  compound 
to  be  thus  used,  it  must  be  borne  in  mind,  that  the  paste  must 
not  be  more  stubborn  in  resisting  fire  than  the  seggars ,  or 
vessels  wherein  it  is  inclosed  during  the  baking,  and  no  greater 
proportion  of  any  substance  that  promotes  fusion  must  he  used 
than  can  be  supported  by  the  clay  without  having  its  cohesive¬ 
ness  greatly  diminished. 

The  porcelain  earth  used  in  Berlin  is  compounded  with  sili- 
cious  sand  and  sulphate  of  lime  in  crystals.  The  constituents 
of  their  flux  are  varied  in  the  proportions  according  to  the 
quality  of  the  ware  it  is  intended  to  produce.  In  the  greater 
part  of  the  German  manufactories  felspar  is  used,  and  some 
employ  a  calcareous  sand. 

When  tender  porcelain  was  made  in  the  works  at  Sevres,  a 
small  portion  of  arsenic  entered  into  its  composition.  This  was 
found  very  hurtful  to  the  workmen.  Few  of  the  turners  or 
moulders,  after  following  their  employment  for  some  years,  es¬ 
caped  severe  pulmonary  complaints ;  and  to  this  disadvantage  is 
ascribed  the  order  of  the  French  government  under  which  this 
branch  of  the  manufacture  has  been  discontinued  in  that  estab¬ 
lishment. 

Individual  manufacturers  of  porcelain  in  France  avoid  all  the 
labor  of  preparing  their  materials,  and  purchase  these  in  a 
state  of  readiness  from  establishments  at  Limoges  where  the 
best  porcelain  earth  is  found.  The  price  of  the  compound, 
when  delivered  in  Paris,  or  at  an  equal  distance  from  the  place 
of  preparation,  does  not  exceed  three  sous — about  one  penny 
halfpenny  of  our  money — per  pound. 

This  arrangement  must  considerably  simplify  the  operations 
of  the  manufacturers,  and  lessens  the  amount  of  capital  which 
they  must  employ  in  the  establishment  of  their  works ;  but  it 
is  doubtful  whether  the  accompanying  disadvantages  are  not 
fully  equivalent  to  these  benefits.  There  are  many  reasons  to 
render  such  a  plan  ineligible  in  this  country. 


48 


PORCELAIN  MANUFACTURE. 


CHAP.  IV. 


CHAP.  IV. 

ON  THE  FORMATION  OF  UTENSILS. 

Throwing. — Potter’s  Lathe. — Thrower. — Mode  of  Proceeding. — Profiles.— 
Slurry. — Gauges. — Turning  Lathe. — Turning  and  Smoothing. — Moulding 
Dishes.  &c. — Tools. — Steam  Machinery. — Engine-Lathe. — Milled  Edges. — 
Handler.— Formation  of  Handles,  Spouts,  &c.— Pressing.— Small  Orna¬ 
mental  Figures. — Mode  of  affixing  them. — Method  of  making  Moulds. — 
Boiled  Plaster. — Great  use  of  Gypsum  in  making  Moulds. — Stoves. — Mod¬ 
elling. — Qualifications  requisite  for  a  Modeller. — Increasing  Skill  of  Art¬ 
ists. — Fostered  by  Mr.  Wedgwood. — Mould-Maker. — Method  of  his  Work¬ 
ing. — Casting. — Carefulness  required  in  Drying. 

The  operation  of  throwing  consists  in  shaping  such  vessels 
as  have  a  circular  form,  and  is  performed  upon  a  machine  call¬ 
ed  a  potter’s  lathe. 

This  consists  of  an  upright  shaft,  about  the  height  of  a  com¬ 
mon  table,  on  the  top  of  which  is  fixed  a  circular  piece  of  wood, 
whose  breadth  is  sufficient  to  support  the  widest  vessel  that  is 
to  be  made.  The  bottom  of  the  shaft  runs  in  a  step,  and  the 
upper  part  in  a  socket  a  little  below  the  circular  board,  so  that 


Fig.  1- 


the  shaft  and  board  turn  together.  The  shaft  has  a  pulley  fixed 
upon  it  by  means  of  which  it  is  turned,  an  endless  band  passing 
round  the  pulley  from  a  wheel  placed  at  a  short  distance,  and 
which  is  ten  times  the  diameter  of  the  pulley ;  this  wheel  when 
turned  by  a  handle  sets  the  lathe  in  motion. 

The  clay  to  be  thrown  is  first  cut  and  weighed  and  formed 
into  a  ball.  It  is  then  placed  on  the  face  of  the  circular  board, 
which  being  put  in  motion,  the  thrower ,  dipping  his  hands  from 
time  to  time  into  water,  or  slip,  that  the  clay  may  not  adhere  to 
them,  fashions  it  first  into  a  long  thin  column,  which  he  forces 
again  down  into  a  lump,  and  continues  these  operations  until  as¬ 
sured  that  no  air-bubbles  can  possibly  remain  in  the  body  of  the 
clay.  He  then  directs  that  the  speed  of  the  wheel  shall  be  mode- 


CHAP.  IV. 


FORMATION  OF  UTENSILS. 


49 


rated,  and  proceeds  to  give  the  first  form  to  the  vessel.  This 
is  done  either  by  his  fingers  alone,  or  with  the  aid  of  an  instru¬ 
ment  shaped  according  to  the  desired  form.  The  instruments 
employed  for  this  purpose  are  called  profiles  or  ribs.  By  the 
assistance  of  one  of  these,  the  inside  is  smoothed  and  made  to 
assume  the  requisite  shape,  and  any  inequalities,  technically 
called  slurry,  are  removed.  When  it  is  wished  to  make  any 
number  of  vessels  exactly  similar  to  each  other  in  shape  and 
dimensions,  certain  pegs  are  fixed  as  a  gauge  without  the  cir¬ 
cumference  of  the  revolving  board,  but  placed  in  such  a  man¬ 
ner,  that  whenever  the  plastic  clay  is  brought  to  coincide  at 
the  requisite  points  with  the  gauge,  the  thrower  knows  that 
the  article  has  attained  the  proper  dimensions. 

In  this  manner  most  circular-shaped  vessels  are  formed. 
When  finished  to  the  artist’s  satisfaction,  he  proceeds  to  re¬ 
move  his  work,  cutting  it  from  the  lathe  by  passing  a  thin  brass 
wire  through  the  lowest  part  of  the  clay.  The  vessel  is  then 
lifted  off  and  placed  on  a  board  or  shelf,  where  it  is  left  to  dry 
partially  before  it  is  farther  smoothed  and  shaped  in  the  turn¬ 
ing-lathe. 

When  the  vessel  is  so  far  dried  as  to  be  in  that  particular 
state  of  hardness  well  known  to  the  workmen,  and  which  is 
called  the  green  state,  it  is  in  the  most  favorable  circumstances 
for  the  performance  of  the  remaining  operations  of  turning  and 
smoothing,  for  being  furnished  with  handles,  spouts,  and  such 
appendages  as  cannot  be  affixed  in  its  first  formation. 

For  making  circular  dishes,  plates,  saucers,  or  shallow  bowls, 
and  other  vessels  of  that  class,  a  plaster  mould  is  used.  This 
is  slightly  sprinkled  with  powdered  porcelain,  sifted  through  a 
fine  cloth,  and  placed  on  the  block  which  surmounts  the  upright 
spindle  of  the  lathe.  The  block  being  then  set  in  motion,  the 
clay  is  fashioned  in  the  first  place  by  the  hand  of  the  workman, 
which  presses  it  against  the  mould,  and  afterwards  with  a  pro¬ 
file  to  give  the  requisite  internal  form.  If  any  ledge  or  foot  is 
required,  it  is  affixed  afterwards  with  slip,  in  the  manner  here¬ 
after  described  as  employed  for  joining  handles  and  spouts.  All 
superfluous  parts  are  cut  away,  and  the  whole  is  finished  by 
means  of  a  horn  tool  and  a  damp  sponge.  When  sufficiently 
dry  to  be  taken  from  the  moulds,  the  edges  are  pared  with  a 
sharp  knife,  and  the  pieces  are  slightly  polished  by  the  hand. 
After  this,  they  are  placed  in  piles  of  four,  six,  ten,  or  more,  ac¬ 
cording  to  their  weight  and  solidity,  and  are  left  to  harden, 
preparatory  to  their  being  put  in  the  oven. 

The  turning-lathe  of  the  potter  is  similar  to  that  used  by  the 
turner  in  wood.  The  end  of  the  spindle  has  a  screw  thread, 
upon  which  are  screwed  chucks  of  wood,  tapered  in  their  form, 

E 


PORCELAIN  MANUFACTURE. 


CHAP.  IV. 


60 


and  differing  in  their  diameters  according  to  the  size  of  the  ar¬ 
ticle  to  be  turned.  The  tools  employed  are  of  different  sizes, 
from  a  quarter  of  an  inch  to  two  inches  broad,  and  six  inches 
long :  they  are  made  of  iron,  the  cutting  end  being  turned  up 
about  a  quarter  of  an  inch,  and  ground  to  a  good  edge. 

The  vessel  to  be  turned  being  fixed  upon  the  chuck,  and  mo¬ 
tion  communicated  to  the  lathe,  the  turner  proceeds  to  reduce 
the  substance  of  the  clay  in  such  parts  as  are  required,  to  form 
rings  and  rims  upon  the  vessel,  and  generally  to  attend  to  those 
little  niceties  of  shape  which  are  not  easily  attainable  on  the 
throwing-lathe.  When  this  is  completed,  a  contrary  motion  is 
given  to  the  spindle,  the  turner  applies  the  flat  part  of  his  tool 
to  the  vessel,  and  using  a  gentle  pressure,  produces  the  requi¬ 
site  smoothness  of  surface  and  solidity  of  texture. 

In  those  considerable  establishments  which  are  furnished 
with  a  steam-engine,  the  throwing  and  turning  lathes  are  both 
actuated  by  it.  To  the  first  of  these  machines  motion  is  then 
given  by  means  of  two  upright  cones,  placed  opposite  to  each 
other ;  the  apex  of  the  one  answering  to  the  base  of  the  other. 
One  of  these  cones  receives  motion  directly  from  the  engine, 
and  communicates  it  by  means  of  a  leather  strap  to  the  other. 
By  this  arrangement  the  horizontal  strap  has  always  an  equal 
tension  to  whichever  parts  of  the  cones  it  is  applied,  the  en¬ 
largement  of  the  one  answering  to  the  diminishing  diameter  of 
the  other ;  but  the  speed  given  to  the  lathe  will  depend  upon 
the  position  on  the  driving  cone  which  the  strap  occupies:  if 
this  is  at  the  small  part,  the  driven  cone,  and  consequently  the 
revolving-board  of  the  lathe,  will  travel  more  slowly,  and  its 
revolutions  will,  on  the  other  hand,  be  accelerated  in  proportion 
as  the  strap  is  made  to  occupy  the  larger  part  of  the  driving 
cone.  When  the  strap  takes  its  position  on  the  largest  part  of 
this,  it  will  apply  to  the  smallest  part  of  the  driven  cone,  and 
the  speed  of  the  lathe  will  be  at  its  maximum.  The  position  of 
the  strap  upon  the  cone  is  regulated  at  pleasure  by  a  winch,  a 
boy  in  attendance  upon  which  follows  the  directions  of  the 
thrower.  When  the  article  is  finished,  the  strap  is  thrown  off 
the  driving  cone,  and  the  motion  of  the  lathe  of  course  ceases. 

The  turning  lathes,  when  actuated  by  the  steam-engine,  are 
arranged  in  a  row,  the  whole  length  of  the  room,  through 
which  runs  a  horizontal  shaft,  and  this  has  fixed  upon  it,  oppo¬ 
site  to  each  lathe,  a  drum,  straps  on  which  connect  the  shaft 
with  the  lathes.  The  speed  of  the  lathes  is  regulated  by  pro¬ 
viding  pulleys  of  different  sizes,  upon  any  one  of  which  the 
strap  may  be  guided  by  the  turner  during  the  revolutions  of  the 
spindle.  When  the  turning  of  the  vessel  is  finished,  the  strap 
is  transferred  to  another  pulley  connected  by  a  crossed  6trap 


51 


CHAP.  IV.  FORMATION  OF  UTENSILS. 

with  the  spindle,  which  by  that  means  has  a  reversed  motion 
communicated  to  it,  and  the  article  under  operation  is  smooth¬ 
ed  and  pdished  in  the  manner  already  described. 

A  milled  edge  is  given  to  earthenware  in  what  is  called  an 
engine  lathe ,  where,  in  addition  to  the  rotary  motion  communi¬ 
cated  to  the  article,  it  has  likewise  a  horizontal  movement  to 
and  fro,  enabling  the  workman  to  make  the  requisite  incisions 
at  proper  and  definite  intervals. 

When  the  vessels  are  taken  from  the  turning-lathe,  they  are 
delivered  to  the  handler,  who  fixes  upon  them  handles,  spouts, 
and  other  appendages  of  that  nature.  These  are  affixed  to  the 
vessels  by  means  of  slip,  with  which  the  parts  brought  into  con¬ 
tact  are  moistened.  Being  then  left  for  a  short  time  to  dry,  the 
junction  is  found  to  be  perfect and  with  a  knife  the  superflu¬ 
ous  clay  is  removed  from  about  it :  the  whole  vessel  is  next 
cleaned  with  a  damp  sponge,  which  moistens  the  whole  equally, 
and  gives  uniformity  to  its  appearance. 

Handles,  spouts,  and  objects  of  that  nature  are  made  with,  the 
aid  of  a  press,  consisting  of  a  small  metallic  cylinder,  which  has 
an  aperture  in  the  centre  of  its  bottom,  to  which  plugs  with  dif¬ 
ferently  shaped  orifices  are  fitted.  It  has  also  a  piston,  actuated 
by  a  screw,  which  works  through  an  iron  bow  attached  to  oppo¬ 
site  sides  of  the  cylinder.  The  aperture  in  the  bottom  being 
furnished  with  a  plug  of  the  desired  form,  and  the  cylinder 
charged  with  clay,  the  piston  is  inserted,  and  by  the  turning  of 
the  screw  is  forced  down  upon  the  clay,  causing  it  to  protrude 
through  the  aperture  in  the  proper  shape.  This  being  cut  into 
lengths,  and  bent  into  the  required  form,  is,  when  sufficiently 
dry,  affixed  to  the  vessel  as  already  mentioned.  If  the  clay  is 
required  to  take  a  hollow  cylindrical  form,  as  it  must  for  spouts, 
a  pin  of  the  same  diameter  as  it  is  wished  to  give  the  tube  is 
fixed  above  the  centre  of  the  plug.  It  is  obvious  that  some  or¬ 
namented  spouts  cannot  be  made  by  this  means.  For  forming 
such,  two  moulds  of  plaster  must  be  prepared  in  the  manner 
hereafter  described,  one  half  of  the  figure  being  impressed  in 
each  of  the  moulds,  which  must  fit  together  accurately.  Clay 
is  then  forced  into  each  mould,  and  the  superfluous  quantity 
being  cut  away,  leaving  still  a  small  portion  above  the  level  of 
the  moulds,  the  two  are  brought  firmly  together  to  unite  the 
two  halves  of  the  article.  The  mould  is  then  divided,  the  clay 
is  removed,  and  finished  as  to  its  form  with  suitable  tools  by  the 
workman.  This  is  the  operation  known  under  the  name  of 
pressing.  The  moulds  for  the  purpose  are  made  with  plaster 
of  Paris,  (gypsum,  or  the  native  sulphate  of  lime,)  the  peculiar 
fitness  of  which  material  for  the  purposes,  arises  from  its  prop¬ 
erty  of  absorbing  water  with  very  great  rapidity,  so  that  the 


52 


PORCELAIN  MANUFACTURE. 


CHAP.  IV. 


ware  inclosed  witliin  it  speedily  dries  in  a  sufficient  degree  to 
deliver  itself  (according  to  the  workman’s  phrase)  easily  from 
the  mould. 

Small  ornaments,  such  as  figures,  animals,  foliage,  and  the 
like,  are  more  conveniently  made  by  pressing  the  clay  in  pias¬ 
ter  moulds,  or  otherwise  these  are  made  of  copper,  which  must 
previously  be  slightly  smeared  with  oil,  in  order  to  insure  the 
easy  delivery  of  the  ornaments.  These  are  then  affixed  to  the 
vessel  by  means  of  slip,  according  to  the  method  already  de¬ 
scribed.  It  is  in  this  manner  that  drinking  jugs  are  so  com¬ 
monly  ornamented  with  figures  in  relief. 

In  order  to  prepare  the  plaster  for  making  moulds,  it  is  first 
ground  between  a  pair  of  stones,  in  a  mill  exactly  similar  to  that 
employed  for  grinding  wheat ;  it  is  next  boiled  in  order  to  drive 
off-  the  water  which  forms  a  considerable  constituent  part  of  its 
natural  substance.  There  is  an  appearance  of  absurdity  in  thus 
speaking  of  boiling  a  dry  earthy  substance ;  but  the  workmen 
who  use  the  term,  are  not  very  far  wrong  in  their  expression. 
To  all  appearance,  ebullition  goes  rapidly  on  in  this  operation, 
and  there  is  a  disengagement  of  steam  as  in  the  boiling  of  watery 
fluids.  When  this  process  is  completed,  the  substance  is  al¬ 
ways  called  boiled  plaster.  The  evaporation  is  conducted  in 
long  brick  troughs,  having  a  fire  flue  running  under  their  en- 
tire  length,  in  a  manner  similar  to  the  slip-kiln.  The  man  who 
superintends  the  process,  is  obliged  to  wear  a  handkerchief  over 
his  mouth  and  nostrils,  to  prevent  the  passage  of  any  particles 
of  the  gypsum  to  his  lungs,  or  stomach,  such  a  circumstance 
having  been  found  very  prejudicial  to  health. 

The  plaster  when  thus  deprived  of  its  water  becomes  a  soft 
impalpable  powder,  but  when  its  natural  proportion  of  water  is 
again  added,  so  strong  is  its  affinity  for  that  liquid,  and  such  its 
capacity  for  again  combining  with  itself  that  portion  of  which  it 
has  been  deprived,  that  it  attracts  and  condenses  the  whole,  and 
will  immediately  set  into  a  hard  and  very  compact  mass,  pecu¬ 
liarly  suitable  for  the  purpose  here  required. 

The  consumption  of  plaster  cf  Paris,  in  making  moulds  for 
plates  and  dishes  is  so  considerable,  that  in  the  district  compre¬ 
hending  the  Potteries,  in  Staffordshire,  many  tons  are  annually 
worn  out  and  thrown  away  as  useless. 

Articles  placed  in  these  moulds  part  with  moisture  so  rapidly, 
that  when  put  in  a  very  temperate  stove,  they  will  become  dry 
enough  for  removal  in  two  hours,  and  each  individual  mould  is 
capable  of  being  used  for  forming  four  or  five  different  articles 
in  the  course  of  a  working  day  of  twelve  hours.  The  stove 
wherein  these  moulds,  with  their  contents,  are  placed  to  dry,  is 
a  small  room  built  with  bricks,  and  having  wooden  shelves 


CHAP.  IV. 


FORMATION  OF  UTENSILS. 


53 


ranged  round  it,  and  over  one  another  from  the  floor  nearly  to 
the  ceiling;  it  is  heated  by  warm  air  conducted  through  it  in 
an  iron  pipe. 

Moulds  for  producing  simple  wares,  such  as  plates  and  dishes, 
and  generally  for  such  objects  as  are  formed  by  pressing,  are 
simple  in  their  construction ;  but  others,  which  are  used  for  the 
third  department,  that  of  casting,  call  for  much  more  art  and 
skill  for  their  invention  and  execution.  For  these,  the  taste  of 
the  modeller  is  put  in  requisition,  calling  for  the  exertion  on  his 
part,  of  a  high  degree  of  skill  and  ingenuity  in  forming  patterns, 
and  adapting  to  them  appropriate  ornaments.  To  be  a  perfect 
modeller,  in  the  higher  branches  of  the  art,  a  man  should  have 
an  acquaintance  with  the  best  productions  of  the  classic  climes 
of  Greece  and  Rome ;  he  should  be  master  of  a  competent 
knowledge  of  the  art  of  design ;  his  fancy  glowing  with  ori¬ 
ginality,  tempered  and  guided  by  elegance  and  propriety  of 
feeling,  and  restrained  by  correctness  of  taste  and  judo-ment. 
To  a  man  thus  gifted,  the  plastic  and  well-tempered  material 
wherewith  he  works  offers  little  of  difficulty  in  the  execution 
of  his  conceptions. 

In  the  most  considerable  works,  and  where  the  proprietors 
are  ambitious  of  excelling,  modellers  are  kept  in  constant  em¬ 
ployment.  Other  manufacturers  content  themselves  with  buy¬ 
ing  new  moulds  from  artists  who  compose  them  on  speculation, 
and  who  are  sometimes  so  little  scrupulous  as  to  dispose  of  the 
same  pattern  to  several  different  purchasers. 

For  want  of  due  encouragement,  high  degrees  of  excellence 
in  this  art  were  formerly  not  of  frequent  occurrence.  Mr. 
Wedgwood,  to  whom  the  porcelain  manufacture  of  England 
owes  so  many  and  such  various  benefits,  proved  that  talent  in 
this  branch  of  art  needed  only  for  its  development  to  be  fostered 
and  encouraged  with  liberality.  This  patriotic  individual  paid 
the  sum  of  four  hundred  pounds  to  Mr.  Webber  for  modelling 
the  Portland  or  Barberini  vase,  although  the  work  called  for  no 
original  or  inventive  powers.  Since  that  time,  English  model¬ 
lers  have  attained  to  such  a  degree  of  excellence,  that  it  is  said 
any  good  modeller,  with  one  qualified  assistant,  would  be  able 
to  achieve,  in  the  short  space  of  two  weeks,  the  task  which  oc¬ 
cupied  Mr.  Webber  for  many  months,  and  which  was  viewed, 
at  the  time,  as  an  honorable  proof  of  both  his  talent  and  in¬ 
dustry. 

The  model,  when  moulded  by  the  hand,  must  be  trimmed, 
carved,  touched,  and  retouched  with  suitable  tools,  constructed 
of  metal  or  wood,  and  sometimes  even  of  ivory,  for  the  more 
perfect  finishing  of  the  whole  composition. 

When  thus  completed,  the  model  passes  into  the  hands  of  the 

E  2 


64  PORCELAIN  MANUFACTURE.  CHAP.  IV. 

mould-maker,  whose  occupation  is  quite  mechanical  and  distinct 
from  that  of  the  modeller.  A  strong  casting  of  clay  is  first 
formed  and  securely  fixed  round  the  model,  leaving  sufficient 
space  between  for  the  substance  of  the  mould.  Proper  propor¬ 
tions  of  plaster  of  Paris  and  water  are  then  placed  in  a  jug,  and 
the  mixture  is  briskly  stirred,  so  that  the  water  may  thoroughly 
pervade  the  whole,  which  is  then  poured  gently  upon  and 
around  the  model,  covering  it  in  every  part  to  the  requisite  de¬ 
gree  of  thickness.  Upon  this  some  heat  is  sensibly  given  out 
by  the  plaster,  and  the  whole  is  very  shortly  converted  into  a 
hard  compact  mass,  easily  separable  from  the  model,  and  found 
to  exhibit  a  perfect  impression  of  its  form,  and  the  minutest 
niceties  of  its  ornaments.  The  mould  is,  after  this,  placed  in  a 
stove  to  be  thoroughly  dried,  and  is  then  fit  for  use. 

Many  articles  were  formerly  made  by  casting,  which  are 
now  produced  by  the  operation  of  pressing  last  described. 
Casting  is  now  employed  only  for  the  formation  of  irregular¬ 
shaped  vessels,  where  much  nicety  is  required,  and  which  need 
not  have  much  strength.  The  casting  operation  is  performed 
by  intimately  mixing  the  united  clay  and  flint  with  very  pure 
water  to  the  consistence  of  cream.  On  pouring  this  dilution 
into  the  mould,  the  plaster  quickly  absorbs  water  from  that  por¬ 
tion  which  lies  in  contact  with  its  surface,  hardening  it  to  such 
a  degree,  that  on  the  central  and  still  fluid  part  being  poured  off, 
a  coating  of  clay  will  remain  attached  to  the  mould.  This 
coating  having  been  allowed  further  to  dry  during  a  short  time, 
a  second  charge  of  diluted  clay,  but  the  consistence  of  which  is 
much  greater  than  the  creamy  fluid  first  used,  is  poured  in,  and 
adds  to  the  substance  of  the  first  deposit.  Having  remained  in 
the  mould  sufficiently  long  for  this  purpose,  the  remainder  of 
the  semi-fluid  is  poured  ofl,  and  the  mould,  with  its  contents,  is 
set  in  a  stove :  when  sufficiently  dry  to  allow  of  separation,  the 
article  is  taken  from  the  mould,  and  left  until  it  is  brought  to 
the  green  state,  when  all  imperfections  are  rectified  by  the 
workman,  whose  skill  is  exerted  to  render  the  vessel  as  smooth 
and  as  perfect  as  possible. 

It  is  essential  to  the  excellence  of  all  kinds  of  earthenware, 
that  the  means  used  for  drying  it  previous  to  the  baking  should 
produce  an  uniform  evaporation  throughout  its  entire  substance. 
If  too  much  heat  were  artificially  employed,  the  surface  might 
be  hardened,  while  the  internal  part  remained  moist;  and  this 
would  be  attended  with  disastrous  consequences  in  the  oven, 
owing  to  the  unequal  contraction  that  would  then  ensue.  It  is,  for 
this  reason,  necessary  to  allow  time  for  the  gradual  dispersion 
of  moisture,  which,  however,  may  be  advantageously  expedited, 


CHAP.  V.  OF  FIRING  AND  GLAZING.  55 

by  placing  the  pieces  upon  plaster  shelves,  whose  absorbent 
property  would  occasion  the  requisite  drying  in  a  shorter  time, 
and  with  increased  regularity  and  uniformity. 

CHAP.  V. 

ON  THE  PROCESSES  OF  FIRING  AND  GLAZING. 

Seggars.— Proper  Materials  for  these  wanting  in  England. — Not  so  in 
France.— Nungarrow  Work.— Why  discontinued.— Great  Estimation  of 
its  Wares.— Cause  of  Superiority.— Use  of  Seggars.— Their  Forms  — Mode 
of  using  them.— Sevres  Manufactory.— Improved  Furnace— Its  advan¬ 
tages.— Description. — Chinese  Method  of  Firing.— Construction  of  their 
Kilns. — Care  required  in  Baking. — Duration  of  Process. — Oven -Man. — 
Trial  Pieces. — Annealing.— Biscuit. — Wine  Coolers. — Glazing. — Compo¬ 
sition  of  Raw  Glazes. — Bad  effects  of  some  of  thesp  to  the  Public. — To  the 
Workmen. — Pernicious  use  of  Ardent  Spirits. — Glazes  invented  by  M. 
Chaptul. — Bv  Mr.  Rose. — Porcelain  Glazes. — French  Glazes. — Palissy. — 
His  Experiments  on  Enamelling.— His  Perseverance  and  Sufferings.— His 
Success,  and  continued  Firmness  under  Persecution. — Inferior  Glazes.— 
Low-priced  Wares.— Gloss-Oven.— Regulation  of  Temperature.— Qualities 
that  determine  the  Excellence  of  Porcelain.— Stone-Ware. — Its  Compo¬ 
sition — Lambeth  Potteries. — Modes  of  Glazing. 

In  the  state  whereto  the  vessels  are  now  brought,  they  are 
ready  to  undergo  the  first  application  of  fire  in  the  oven.  For 
this  purpose  they  are  placed  in  deep  boxes  called  seggars, 
made  of  a  mixture  of  fire  clay  and  old  ground  seggars,  which 
should  be  well  baked,  and  capable  of  sustaining  the  most  in¬ 
tense  degree  of  heat  without  being  fused.  The  porcelain 
manufactures  of  this  country  labor  under  a  considerable  disad¬ 
vantage  in  this  respect,  being  unable  to  procure  materials  for 
the  construction  of  these  cases  that  will  sufficiently  withstand 
the  direct  heat  of  the  furnace.  This  difficulty  does  not  occur 
in  France,  a  fact  which  is  assigned  by  our  potters  as  one  prin¬ 
cipal  reason  for  the  better  quality  of  French  porcelain. 

A  porcelain  manufactory  was  carried  on  some  years  since 
at  Nungarrow  in  Wales,  but  which  is  now  discontinued.  The 
wares  produced  in  these  works  were  perhaps  superior  in  quality 
to  any  porcelain  that  hitherto  has  been  made  in  any  other  part 
of  this  country.  No  expense  was  spared  either  in  the  procure¬ 
ment  of  materials,  or  in  conducting  the  various  processes ;  and 
the  want  of  success  on  the  part  of  the  spirited  proprietors  is 
referrible  solely  to  the  deficiency  of  public  patronage,  it  being 
found  impossible  to  procure  a  price  for  the  goods  which  could 
adequately  meet  the  cost  of  their  manufacture.  Since  the  dis¬ 
continuance  of  this  establishment,  the  excellent  quality  of  its 
wares  has  been  more  justly  estimated,  and  the  prices  which 
are  now  eagerly  given  by  amateurs  and  collectors  for  pieces 


56 


PORCELAIN  MANUFACTURE. 


CHAP.  V. 


of  Nungarrow  porcelain,  are  out  of  all  proportion  greater  than 
were  originally  demanded  by  the  makers. 

The  materials  of  which  this  porcelain  is  composed  are  of  the 
most  refractory  quality,  and  it  is  understood  that  success  in 
their  conversion  was  only  attained  through  the  expensive 
measure  of  sacrificing  the  seggars  employed,  which,  owing  to 
the  high  degree  of  heat  whereto  they  were  exposed,  could 
never  be  placed  a  second  time  in  the  furnace. 

The  office  of  the  seggars  is  to  protect  the  wares  while  being 
baked  from  the  direct  application  of  flame  and  from  smoke  ; 
the  heat  is  somewhat  modified  in  its  transmission  through 
them,  and  applies  itself  uniformly  to  each  part  of  the  vessels. 
The  cases  are  made  of  various  shapes,  sizes,  and  depths,  to  suit 
the  different  pieces  they  are  to  contain,  and  some  judgment  is 
required  in  their  composition,  to  fit  them  for  the  several  kinds 
of  pottery. 

To  prevent  any  adhesion  of  the  pieces  to  the  seggars,  the 
flat  bottom  of  each  is  covered  with  a  thin  layer  of  fine  white 
sand.  That  this  even  may  not  adhere  to  the  porcelain,  the 
Chinese  strew  over  the  sand  some  dry  kao-lin  in  powder. 
Pieces  of  any  considerable  size  must  each  be  inclosed  in  a  sep¬ 
arate  case,  but  smaller  objects,  such  as  cups  or  saucers,  may  be 
placed  together  to  the  number  of  six  or  twelve,  but  in  no  case 
must  one  piece  be  placed  in  or  on  another  in  the  seggar,  and 
all  must  be  so  arranged  that  the  heat  will  be  equally  applied  to 
every  part  of  each. 

In  some  instances  seggars  are  made  having  triangular  holes 
in  their  sides,  for  the  purpose  of  admitting  prisms  of  the  same 
form,  which  are  inserted  therein,  horizontally,  in  order  to  sup¬ 
port  a  greater  number  of  pieces  in  a  state  of  isolation  within 
each  case  than  could  be  accomplished  by  other  means.  The 
prisms  thus  used  must  be  compounded  of  the  same  materials  as 
the  cases  themselves.  This  course  is  not  pursued  except  with 
common  articles,  and  is  adopted  with  the  intention  of  economiz¬ 
ing  the  time,  space,  and  fuel  employed  for  baking  them. 

If  the  clay  whereof  they  are  composed  be  well  chosen  and 
carefully  managed,  the  seggars  may  be  placed  from  fifteen  to 
twenty  several  times  in  the  furnace  before  they  are  rendered 
useless. 

Some  art  is  required  so  to  dispose  the  cases  within  the  oven, 
with  reference  to  their  shape,  size,  and  the  objects  they  con¬ 
tain,  that  the  heat  shall  be  distributed  as  faithfully  as  possible, 
and  that  the  sufficient  baking  of  all  the  different-sized  vessels 
shall  be  accomplished  during  the  same  time.  The  largest  and 
coarsest  pieces  are  usually  placed  on  the  floor  of  the  oven, 
which  must  be  previously  covered  with  a  layer  of  sand.  If  the 


CHAP.  V. 


OF  FIRING  AND  GLAZING. 


57 


heat  be  not  faithfully  distributed  through  the  whole  area 
some  pieces  would  be  injured  by  excessive  firing,  while  others 
would  be  inadequately  baked.  The  bottoms  of  the  sepals 
being  flat  each  as  it  is  placed  upon  another,  forms  a  cover  to 
that  beneath,  and  the  entrance  of  smoke  is  further  prevented 
by  placing  a  ring  of  soft  clay  on  the  upper  rim  of  each  case. 
In  tms  manner  the  seggars  are  built  one  upon  another  untii 
they  reach  nearly  to  the  top  of  the  oven  :  the  upper  seggar  £ 
each  pfie  IS  always  empty.  Each  of  these  piles,  as  it  stahds  is 
caHed  a  bung ;  in  building  them  up,  intermediate  spaces  ’of 

throuohout  mUSt  be  lett  f°r  the  circuJation  of  heated  air 

the  privijefffs  50  lon§-  enjoyed  by  the  royal  manu- 

ctoiy  at  Sevres,  and  which  were  accompanied  by  correspond- 

flTuChT  pkCedK  by  tbe  French  governmentyupon  prwa'e 
establishments,  must  have  been  upon  the  whole  prejudicial  to 
the  progress  of  the  art  in  France,  these  regulations  had  yet  in 
some  respects  a  contrary  tendency.  Being  secured  in  a^reat 
degree  from  the  effects  of  competition  from  without,  the  di¬ 
rectors  of  the  royal  works  were  enabled  to  prosecute  experi¬ 
ments  with  regard  to  improvements  in  their  utensils  and  pro- 
f  ssesf  Prom  ^e  adoption  of  which  they  might  otherwise  have 

nea?  f n7  cons;deratlons  of  expense.  Suggestions  ap¬ 
pear  to  have  been  continually  made,  having  such  improve¬ 
ments  for  their  object,  by  men  who  enjoyed  the  highest  scien- 

dtJced  °nS  ’  and  the  fU,CCeSS  °f  plans  thus  Proii0sed.  con¬ 
duced  to  the  increasing  celebrity  of  the  establishment 

formTf  0  lers’  “*1  d|.MontlPrny  and  Macquer  contrived  a 
form  of  furnace,  which  effected  at  the  time  of  its  adoption  a 
very  great  advantage.  In  that  previously  used  (and  the  con¬ 
struction  of  which  had  been  copied  from  those  employed  in 
Saxony,)  the  heat  was  so  unequally  distributed,  that  it  was 
necessary  to  vary  the  composition  of  the  porcelain  so  as  to  ren- 
ler  it  suitable  to  different  parts  of  the  furnace.  The  improve¬ 
ment  here  noticed  occasioned  the  sufficient  equalization  of  heat 
iroughout  its  area,  and  a  great  inconvenience  was  at  once  and 
lompfetely  remedied. 

The  arrangement  whereby  this  important  change  was  ac¬ 
complished  will  be  understood  by  a  reference  to  the  following 
igures,  which  describe  the  elevation,  section,  and  plan  of  the 

,ide  sam®  letters  are  employed  to  denote  similar  parts 
o  the  different  figures.  " 

.  ^is  t}?e  i"ter,ior  area  of  the  kiln.  This  is  fourteen  feet 
ight  inches  high,  and  eight  feet  three  inches  in  diameter: 

|  he  walls  should  be  three  feet  thick.  BBBB  are  four  air-flues 
hiaced  at  equal  distances  m  the  circumference.  CCCC  are 


58  PORCELAIN  MANUFACTURE.  CHAP.  V. 

hearths  one  foot  below  the  base  of  the  kiln:  the  heat  from 
these  passes  towards  its  centre.  DDDD  are  openings,  eigh¬ 
teen  inches  square,  for  the  reception  of  the  fuel.  These  open¬ 
ing-.  2. 


ings  are  provided  with  mouth  pieces  of  plate  iron.  E  is  a 
door-way  in  the  side  of  the  kiln :  its  sill  is  three  feet  above  the 


Fig.  3. 


ground ;  its  width  is  two  feet,  and  its  height  five  feet  sis 
inches.  This  door  is  used  for  the  introduction  of  the  seggan 
within  the  kiln,  after  which  it  must  be  securely  walled  up.  f 
is  a  square  hole,  of  which  there  are  three  in  the  entire  cir¬ 
cumference.  These  are  designed  for  the  introduction  of  trial 
pieces  within  the  kiln :  another  similar  opening  is  left  when 


CHAP.  V.  OP  FIRING  AND  GLAZING.  59 

walling  up  the  door-way  E.  The  whole  of  these  are  provided 
with  clay  stoppers  which  exactly  fill  the  holes,  and  which  have 
projections  whereby  they  can  be  removed  or  replaced  at  plea¬ 
sure.  G  is  the  chimney  in  the  centre  of  the  dome-shaped  roof; 
it  is  of  a  conical  form,  eighteen  inches  diameter  at  the  base,  less¬ 
ening  to  twelve  inches  at  the  top.  HH  represent  four  air- 


Fig.  4. 

a 


loles,  placed  over  the  openings  F.  These  air-holes  serve  to 
livide  the  draught,  and  consequently  to  equalize  the  tempera- 
ure  of  the  kiln.  I  is  a  round  iron  plate,  supported  on  four 
•illars  of  the  same  metal,  and  placed  over  the  chimney  to  de¬ 
end  the  opening. 

When  the  firing  has  been  sufficiently  performed,  no  more 
uel  is  added,  and  so  soon  as  the  smoke  from  that  already  upon 
he  hearths  has  passed  away,  the  mouth  pieces  are  entirely 
losed  to  prevent  the  passage  of  air.  Shortly  after  this,  the 
himney  G  and  the  air-holes  H  are  also  carefully  closed,  and 
le  kiln  is  left,  that  the  cooling  of  its  contents  may  go  forward 
s  slowly  as  possible. 

Previously  to  the  adoption  of  this  improvement,  the  kiln  em- 
loyed  for  baking  porcelain  was  always  made  of  a  rectangular 
>rm,  having  only  one  fire-place  and  one  air-flue,  which  stood 
t  the  side  opposite  to  that  whereon  the  chimney  was  placed : 
a  arrangement  which  rendered  quite  inevitable  the  before- 
lentioned  inconvenience,  arising  from  the  unequal  distribution 
'heat. 


60  PORCELAIN  MANUFACTURE.  CHAP.  V. 

The  extension  of  the  art,  and  the  consequent  competition 
among  the  manufacturers  in  France  since  the  return  of  peace, 
have  compelled  them  to  use  the  utmost  economy  in  their  vari¬ 
ous  processes ;  so  that,  while  the  quality  of  their  goods  has  been 
fully  sustained,  the  prices  have  been  importantly  lowered. 
These  savings  have  been  partly  realized  through  the  increased 
skill  of  the  workmen,  but  are  more  referrible  to  the  smaller 
proportionate  quantity  of  fuel  consumed,  which  has  arisen,  not 
from  any  further  improvement  in  the  form  of  their  kilns,  but 
through  a  better  arrangement  in  filling  them,  whereby  they  are 
now  made  to  contain,  at  each  baking,  nearly  one  third  more  of 
pieces  than  was  formerly  customary. 

The  potter’s  oven  is  now  always  made  of  a  cylindrical  form, 
and  very  similar  to  the  common  kilns  used  for  burning  tiles, 
with  the  external  appearance  of  which  every  one  is  familiarly 
acquainted.  The  furnace  mouths  of  the  oven  are  placed  at  cer¬ 
tain  intervals  around  it;  from  these  the  fire  and  heated  air  pass 
into  horizontal  flues  in  the  floor,  and  thence  ascend  through  all 
the  interstitial  spaces  between  the  bungs,  until  the  surplus  heat 
escapes  through  an  aperture  in  the  centre  of  the  roof. 

The  Chinese  subject  the  greatest  part  of  their  porcelain  to 
only  one  firing,  drying  the  pieces  sufficiently  in  the  air  to  pre¬ 
pare  them  for  glazing.  This  plan  they  are  able  to  pursue,  be¬ 
cause  the  nature  of  their  materials  is  such  as  to  resist  the  en¬ 
trance  of  water.  Their  glaze,  the  composition  of  which  will 
be  hereinafter  described,  is  much  superior  to  any  used  in  Euro¬ 
pean  potteries,  but  requires  the  most  intense  degree  of  heat  for 
its  fusion,  and  considerable  art  is  consequently  required  for  the 
management  of  the  fire,  as  well  as  in  the  construction  of  their 
ovens.  These  are  built  in  a  most  substantial  manner,  so  that 
when  the  fire  is  at  its  greatest  height,  the  hand  may  be  applied 
to  the  outside  without  any  fear  of  burning.  The  draft  is  pro¬ 
moted  by  placing  the  oven  at  the  extreme  end  of  a  long  narrow 
passage,  which  acts  as  a  funnel  in  supplying  air  for  supporting 
combustion,  the  intensity  of  which  is  regulated  by  four  or  more 
side  apertures,  or  registers,  which  are  opened  or  shut  according 
as  the  heat  is  required  to  be  augmented  or  moderated.  The 
hearth  is  placed  in  front,  and  occupies  the  whole  breadth  of  the 
oven.  The  pieces  which  are  placed  in  seggars,  are  artfully 
disposed  in  the  oven,  in  the  manner  already  described  as  follow¬ 
ed  in  England.  When  the  fire  is  lighted,  the  furnace  door  is 
walled  up,  leaving  only  an  aperture  large  enough  for  the  intro¬ 
duction  of  fuel.  The  heat  is  raised  gradually  during  about 
thirty  hours,  after  which  time  fuel  is  incessantly  supplied  by 
two  men,  who  relieve  each  other  at  intervals.  The  wood  used 
for  this  purpose  is  very  carefully  dried  and  cut  into  slender  bil- 


CHAP.  V.  OF  FIRING  AND  GLAZING.  61 

lets  about  one  foot  in  length,  that  their  combustion  may  be  ef¬ 
fected  with  greater  rapidity. 

Great  attention  is  necessary  for  properly  conducting  the  op¬ 
eration  of  baking.  Vauquelin  observes  that  the  heat  must  be 
sufficient  to  expel  all  the  moisture,  and  occasion  the  cohesion 
of  the  parts  whereof  the  paste  is  composed ;  but  that,  if  carried 
too  far,  the  texture  of  the  ware  becomes  too  homogeneal,  and  it 
is  rendered  brittle.  It  requires  a  degree  of  heat  sufficient  to 
melt  silver  (4717°  Fahrenheit)  in  order  to  expel  the  last  portion 
of  water  from  clay :  when  this  has  been  effected,  it  is  found 
that  the  weight  of  alumina  is  diminished  forty-six  per  cent. 

The  process  of  baking  usually  lasts  from  forty-eight  to  fifty 
hours,  during  which  time  the  heat  is  gradually  increased ;  as  it 
would  be  injurious  to  apply  a  very  high  degree  at  first.  In  order 
to  ascertain  when  the  baking  has  been  carried  far  enough,  the 
oven-man  places  trial  pieces  in  different  parts  of  the  oven,  but 
so  disposed  that  they  can  readily  be  taken  out  for  examination. 
These  pieces  are  rings  made  of  common  Staffordshire  fire  clay, 
which  is  found  to  have  the  property  of  changing  its  color  with 
each  accession  of  temperature.  By  comparing  these  rings, 
therefore,  with  pieces  of  the  same  clay  which  have  previously 
been  sufficiently  baked,  and  which  serve  as  a  standard,  the  ac¬ 
tual  progress  of  the  wares  in  the  oven  may  at  any  time  be  ascer¬ 
tained  precisely,  and  with  less  trouble  than  attends  the  use  of 
Wedgwood’s  pyrometer.  When  the  appearance  of  these  trial 
pieces  is  judged  satisfactory,  the  firing  is  discontinued,  the  fur¬ 
nace  and  ash-pit  doors  are  closed,  and  the  oven,  with  its  con¬ 
tents,  left  to  cool  gradually  during  twenty-four  or  thirty  hours. 
It  is  not  necessary  to  delay  the  withdrawing  of  the  pieces  from 
the  oven,  until  they  have  become  quite  cold ;  but  the  sudden 
alteration  of  temperature  would  occasion  them  to  crack,  if  they 
were  taken  out  while  their  heat  was  greatly  above  that  of  the 
atmosphere. 

Some  potters  are  occasionally  tempted,  when  the  furnace 
contains  articles  of  small  value,  to  risk  the  damage  here  men¬ 
tioned.  and  to  withdraw  the  seggars  with  their  contents  with¬ 
out  delay,  their  object  being  to  profit  by  the  heat  of  the  furnace 
either  for  introducing  a  new  charge,  or  for  drying  a  fresh  set  of 
seggars.  No  one,  however,  would  be  so  improvident  as  to  ex¬ 
pose  the  finer  descriptions  of  porcelain  to  this  hazard,  in  order 
to  gain  any  such  immaterial  advantage. 

From  the  similarity  of  its  appearance  to  well-baked  ship 
bread,  the  ware  is  now  called  biscuit.  Its  permeability  to 
water  when  in  this  state  fits  it  for  being  employed  in  cooling 
liquids.  If  previously  soaked  in  water,  the  gradual  evaporation 
from  its  surface  by  means  of  the  air,  causes  an  absorption  of 

F 


62 


PORCELAIN  MANUFACTURE. 


CHAR.  V* 


heat  from  the  surrounding  atmosphere,  which  is  again  supplied 
by  neighboring  objects,  until  an  equilibrium  of  temperature  is 
restored. 

The  proprietors  of  potteries  are  accustomed  to  furnish  vases, 
urns,  and  other  pieces  of  ornamental  shapes,  in  the  state  of  bis¬ 
cuit,  to  ladies  who  exercise  their  taste  and  ingenuity  in  embel¬ 
lishing  them  by  painting  and  gilding.  Being  then  returned  to 
the  manufacturer,  the  glaze  is  applied,  the  baking  is  finished  in 
the  gloss  oven,  and  the  gilding  is  burnished  by  means  that  will 
be  described  hereafter. 

If  it  were  attempted  to  apply  the  glaze  to  articles  of  porcelain 
and  earthenware,  without  their  previous  conversion  into  biscuit, 
their  texture  and  shape  would  be  injured  by  the  absorption  of 
water  from  the  glaze.  Neither  would  it,  for  the  same  reason, 
be  possible  to  ornament  the  ware  by  painting,  or  to  transfer  pat¬ 
terns  to  their  surface  by  printing.  There  is  another  reason 
given  for  the  necessity  of  this  previous  baking,  in  the  greater 
contractibility  of  the  clay  than  of  the  glaze,  which  would  crack 
or  peel  of!'  if  the  limit  of  contraction  had  not  been  previously 
attained.  It  will  be  remembered  that  the  shrinking-  of  clay 
upon  the  application  of  heat  is  permanent,  and  that  no  altera¬ 
tion  of  its  bulk  will  occur,  unless  it  be  subjected  to  a  still  higher 
degree  of  temperature.  By  limiting,  therefore,  the  heat  of  the 
gloss  oven  in  which  the  baking  is  finished,  below  that  applied 
to  the  biscuit,  the  evil  of  cracking  the  glaze,  through  the  con¬ 
traction  of  the  ware,  is  avoided. 

The  glaze  usually  employed  for  common  kinds  of  earthen¬ 
ware  is  compounded  of  litharge  of  lead  and  ground  flints,  in 
the  proportion  of  ten  parts  by  weight  of  the  former  to  four  parts 
of  the  latter.  Cornish  granite  is  sometimes  substituted  for 
flint,  and  used  in  the  proportion  of  eight  parts  to  ten  of  litharge. 
This  method  of  glazing  is  objectionable,  on  account  of  the  injury 
which,  notwithstanding  every  precaution  that  can  be  taken,  it 
occasions,  in  its  application,  to  the  health  of  the  workmen  em¬ 
ployed,  who  frequently  are  seized  with  paralysis;  and  because 
the  lead,  which  is  soluble  by  means  of  acids,  and  highly  pois¬ 
onous,  renders  vessels  thus  glazed  improper  for  preparing  or 
containing  many  articles  of  human  food. 

The  bad  effect  of  raw  glazes  upon  their  health,  is  greatly 
lessened  to  the  workmen  when  they  can  be  brought  to  the  fre¬ 
quent  use  of  ablutions.  In  every  pottery  the  men  employed  in 
glazing  should  be,  and  in  most  establishments  they  are,  plenti¬ 
fully  supplied  with  soap,  which  they  are  enjoined  to  use  on 
every  occasion  of  quitting  their  work.  Unfortunately,  however, 
the  workmen  themselves  have  become  erroneously  impressed 
with  a  belief  in  the  superior  efficacy  of  ardent  spirits  in  ward- 


CHAP.  V. 


OF  FIRING  AND  GLAZING. 


63 


ing  off  or  counteracting  the  poisonous  effects  of  lead,  and  fly  to 
the  use  of  this  as  a  specific,  to  a  degree  which  too  often  proves, 
both  physically  and  morally,  worse  than  the  evil  which  it  is  in¬ 
tended  to  prevent. 

The  mixtures  just  mentioned  are  called  raw  glazes;  their 
employment  is  convenient  to  the  potter  because  of  their  cheap¬ 
ness  and  extreme  fusibility.  Flint,  which  remains  unaffected 
in  the  focus  of  the  most  powerful  lens,  is,  when  combined  with 
lead,  melted  and  vitrified  at  a  comparatively  low  heat.  The 
method  of  using  this  glaze  is  to  reduce  the  ingredients  to  the 
state  of  a  fine  powder,  and  throw  them  into  as  much  water  as 
will  make  them  of  the  consistence  of  thin  cream.  The  mixture 
must  be  well  stirred,  that  the  powders  may  be  always  kept  uni¬ 
formly  blended  throughout  the  fluid.  The  pieces  are  first  brush¬ 
ed  to  free  them  from  dust,  and  then  merely  dipped  into  the  liquid 
and  withdrawn,  when  they  must  be  turned  rapidly  about  in  all 
directions,  that  the  glaze  may  flow  equally  over  the  whole  sur¬ 
face.  The  superfluous  liquid  having  been  allowed  to  drain  oft' 
for  a  few  seconds,  and  the  pieces  having  been  set  on  a  board 
during  a  few  minutes,  theyare  ready  for  insertion  in  the  seggars. 

Chaptal,  in  his  “  Chemistry  applied  to  the  Arts,”  has  given  a 
process  for  forming  white  enamel,  which  answers  well  for  gla¬ 
zing  the  superior  kinds  of  earthenware  and  tender  porcelain. 
Equal  parts  of  lead  and  tin  are  kept  in  fusion  until  completely 
oxidated.  The  powder  thus  formed  is  ground  with  water,  all 
impurities  are  removed  by  repeated  washings,  and  being  dried 
it  is  kept  for  use.  The  whitest  flints  are  then  chosen,  and  fused 
with  carbonate  of  potash,  the  latter  being  in  such  proportion  to 
the  flint,  that  the  mixture  will  be  soluble  in  water.  To  the 
solution  of  flint  thus  made,  muriatic  acid  must,  from  time  to 
time,  be  added,  until  no  further  precipitation  occurs.  The 
precipitate  thus  obtained  is  pure  silex,  which,  being  washed  and 
dried,  is  also  fit  for  use.  If  then  one  part  of  this  silex,  and  one 
part  of  the  metallic  oxide,  be  added  to  two  parts  of  carbonate  of 
potash,  and  the  whole  be  fused  in  a  crucible,  the  mass  need  only 
be  reduced  to  a  fine  powder  to  prepare  it  for  use  in  glazing. 

Mr.  John  Rose,  of  the  porcelain  works  at  Coalport  in  Shrop¬ 
shire,  speaks  in  commendation  of  a  glaze  for  hard  porcelain 
which  he  has  used  for  some  time,  and  which  having  been  ex¬ 
amined  by  competent  artists,  at  the  request  of  the  Society  of 
Arts,  has  been  reported  on  very  favorably.  Mr.  Rose’s  glaze 
is  composed  of  27  parts  of  felspar,  18  of  borax,  4  of  Lynn  sand, 
3  of  nitre,  3  of  soda,  and  3  of  the  China  clay  of  Cornwall.  This 
mixture  is  melted  together  and  ground  to  a  fine  powder ;  3  parts 
of  calcined  borax  being  added  previously  to  the  grinding. 

Glazes  for  porcelain  and  the  finer  kinds  of  earthenware  are 


64 


PORCELAIN  MANUFACTURE. 


CHAP.  V. 


generally  made  with  white  lead,  ground  flints,  ground  flint- 
glass,  and  common  salt;  Lynn  sand  combined  with  soda,  as  a 
flux,  being  frequently  added  to  the  ingredients  just  mentioned. 
Almost  every  manufacturer  uses  a  peculiar  glaze,  the  recipe 
for  which  is  kept  secret  by  him  as  much  as  possible,  under  the 
idea  of  its  superiority  compared  with  that  employed  by  his 
competitors,  so  that  it  is  not  possible  to  state  proportions  with 
accuracy.  The  French  porcelain  makers  have  given  the  com¬ 
position  of  hard  glazes  made  by  them,  which  are  all  said  to  be 
formed  of  flint,  ground  porcelain,  and  crystals  of  calcined  gyp¬ 
sum,  in  the  following  different  proportions : — 

No.  1.  No.  2.  No.  3. 

Calcined  flint  -  --  --  -  -  8  parts  17  parts  11  parts. 

Ground  porcelain  ------  15  16  18 

Crystals  of  calcined  gypsum  -  -  9  7  12 

It  is  necessary  to  vary  the  composition  of  the  glaze,  in  order 

to  suit  the  different  materials  that  form  the  body  of  the  ware, 
since  that  would  be  a  very  fine  glaze  for  one  mixture  of  earths, 
which  would  be  wholly  inappropriate  to  another,  proving  defi¬ 
cient  in  lustre  and  being  liable  to  crack.  Before  adopting  any 
glaze  in  conjunction  with  a  particular  kind  of  ware,  it  is  most 
prudent  to  make  trial  of  it  upon  a  small  scale,  in  order  to  prove 
the  suitableness  of  the  bodies  to  each  other. 

This  branch  of  the  potter’s  art  is  greatly  indebted  to  the  ex¬ 
traordinary  perseverance  of  a  single  man,  Bernard  de  Palissy, 
a  native  of  France,  who  was  born  in  Agen  at  the  close  of  the 
fifteenth  century.  His  parents  occupying  an  humble  station  in 
life,  he  was  entirely  indebted  to  his  own  unquenchable  energy 
and  perseverance  for  the  success  which  crowned  his  industry. 

The  original  occupation  of  Palissy  was  that  of  a  draughts¬ 
man,  to  which  pursuit  he  added  land  surveying.  Accident 
having  thrown  into  his  hands  an  enamelled  cup,  he  was  imme¬ 
diately  seized  with  the  desire  of  improving  the  art,  and  thence¬ 
forward  relinquishing  all  other  occupations,  gave  up  his  whole 
time,  mind,  and  substance,  during  several  years,  to  the  prosecu¬ 
tion  of  experiments  on  the  composition  of  enamel.  He  has 
himself  given  a  narrative  of  his  labors,  sacrifices,  and  suffer¬ 
ings,  during  the  progress  of  his  pursuit,  which  is  intensely  in¬ 
teresting. 

In  this  account,  Palissy  represents  himself  as  alternately 
planning  and  building,  demolishing  and  rebuilding  his  furnace, 
at  every  step  buoyed  up  by  hope,  and  as  often  met,  but  not  sub¬ 
dued,  by  disappointment;  the  object  of  remonstrance  and  de¬ 
rision  to  his  associates,  subject  to  the  expostulations  of  his  wife, 
and  witness  to  the  silent  but  more  eloquent  reproaches  of  his 
children.  In  other  respects  Palissy  proved  himself  an  amiable 


CHAP.  V. 


OP  FIRING  AND  GLAZING.  65 

as  well  as  a  highly-gifted  man ;  for,  notwithstanding  that  his 
efforts  were  ultimately  crowned  by  success, — that  standard 
whereby  the  judgment  of  mankind  is  most  easily  and  therefore 
most  usually  formed, — one  might  hesitate  to  applaud  a  degree 
of  perseverance  which,  for  so  long  a  time,  materially  interfered 
with  the  welfare  of  his  family.  Amidst  all  this  scene  of  de¬ 
privation  and  disappointment,  Palissy  bore  outwardly  a  cheer¬ 
ful  countenance,  and,  throughout  the  lengthened  trial,  confined 
within  the  dungeon  of  his  own  breast  those  feelings  of  bitter- 
ness  which  he  has  so  forcibly  described  as  being  his  portion. 

The  extremities  to  which  he  was  at  one  time  reduced  were 
such,  that  to  provide  fuel  for  feeding  the  furnace,  his  furniture 
and  afterwards  even  some  of  the  woodwork  of  his  dwelling 
was  destroyed ;  and  in  order  to  silence  the  clamor  of  his  assist¬ 
ant  workman  for  the  payment  of  wages,  he  stripped  himself 
of  a  portion  of  his  apparel.  At  length,  however,  these  efforts 
were  rewarded  by  complete  success;  and  fame,  honors,  and  in¬ 
dependence  were  thenceforward  his  attendants  through  a  long 
career  of  useful  occupation. 

Palissy’s  after  pursuits  were  of  a  more  general  character, 
embracing  the  sciences  of  agriculture,  chemistry,  and  natural 
history,  upon  which  subjects  he  both  wrote  and  lectured  with 
ability  and  success. 

Nor  did  the  firmness  of  his  character  forsake  him  for  a  mo¬ 
ment  to  the  end  of  his  life.  Being  a  Protestant,  and  having 
ventured,  in  some  of  his  lectures,  to  promulgate  facts  which 
made  against  the  dogmas  of  the  priests,  he  was,  when  in  his 
ninetieth  year,  dragged  by  the  infuriate  zeal  of  these  fanatics 
to  the  Bastile,  and  died,  with  consistent  firmness,  within  its 
walls.  His  heroic  reply,  while  thus  imprisoned,  to  Henry  III. 
is  above  all  praise.  “  My  good  man,”  said  the  king,  “  if  you 
cannot  conform  yourself  on  the  matter  of  religion,  I  shall  be 
compelled  to  leave  you  in  the  hands  of  my  enemies.” — “  Sire,” 
replied  the  intrepid  old  man,  “  I  was  already  willing  to  surren¬ 
der  my  life,  and  could  any  regret  have  accompanied  the  action, 
it  must  assuredly  have  vanished  upon  hearing  the  great  king 
of  France  say  ‘  I  am  compelled.’  This,  sire,  is  a  condition  to 
which  those  who  force  yOu  to  act  contrary  to  your  own  good 
disposition  can  never  reduce  me;  because  I  am  prepared  for 
death,  and  because  your  whole  people  have  not  the  power  to 
compel  a  simple  potter  to  bend  his  knee  before  images  which 
he  has  made.” 

So  great  is  the  competition  among  potters  in  the  present  day, 
that  means  which  are  injurious  to  their  real  quality  are  fre¬ 
quently  adopted  for  rendering  their  wares  less  costly.  Some 
makers  are  hence  tempted  to  the  employment  of  materials  that 

F  2 


66 


PORCELAIN  MANUFACTURE. 


CHAP.  V. 


will  enable  them,  at  a  moderate  price,  to  furnish  articles  appa¬ 
rently  good,  but  which  will  speedily  prove  defective  when 
brought  into  use.  The  saving  which  the  manufacturer  is  able 
to  effect,  through  the  adoption  of  an  inferior  glaze,  consists 
not  so  much  in  the  actual  cost  of  its  component  parts,  as  in  the 
smaller  quantity  of  fuel  required  for  its  vitrification,  and  in  the 
shorter  period  of  time  demanded  for  its  conversion. 

The"  earthenwares  offered,  at  low  prices,  by  hawkers  and 
pedlars,  and  at  inferior  shops,  are  mostly  composed  of  clay  that 
will  not  bear  a  proper  degree  of  heat  in  the  oven,  and  are 
covered  by  a  glaze  so  tender  as  to  craze  after  a  few  cleansings 
with  hot  water.  If  exposed  to  a  high  temperature,  or  if  acids 
be  applied,  the  glaze  will  be  dissolved,  and  the  vessels  conse¬ 
quently  rendered  useless.  The  quantity  of  lead  which  enters 
into  the  composition  of  the  better  kinds  of  glazes  is  so  small, 
that  the  deteriorating  and  pernicious  effects  which  attend  upon 
the  use  of  raw  glaze  need  not  be  apprehended  from  their  em¬ 
ployment. 

The  seggars  used  to  inclose  the  wares  when  baked  in  the 
gloss  oven,  are  similar  to  those  employed  in  the  first  firing. 
Previous  to  their  insertion,  the  pieces  must  have  the  glaze 
wiped  from  the  parts  which  immediately  rest  upon  the  bottoms 
of  the  seggars,  otherwise  they  would  adhere  and  might  be  bro¬ 
ken  in  their  removal.  The  cases  are  piled  up  in  the  manner 
already  described,  and  just  that  degree  of  heat  must  be  em¬ 
ployed  which  will  give  perfect  fusion  to  the  glaze  and  cause  it 
to  spread  regularly  over  the  surface.  The  temperature,  of 
course,  varies  according  to  the  quality  of  the  articles  and  the 
composition  of  the  glaze;  but,  for  the  reason  already  stated,  it 
must  never  be  carried  beyond  the  degree  to  which  the  biscuit 
has  been  previously  exposed.  In  practice,  the  temperature  of 
the  gloss  oven  is  generally  less  by  about  ten  degrees  of  Wedg¬ 
wood,  or  1300  degrees  of  Fahrenheit’s  scale,  than  the  heat  of 
the  biscuit  oven. 

As  alkaline  substances  are  so  powerfully  instrumental  in 
promoting  the  fusion  of  intractable  bodies,  it  may  be  thought, 
that  by  increasing  their  proportion  when  combined  with  fel¬ 
spar,  glazes  might  be  formed  that  would  fuse  at  a  heat  suffi¬ 
ciently  moderate  for  any  description  of  earthenware,  and  that, 
consequently,  the  use  of  oxide  of  lead,  which  is  so  pernicious, 
might  be  altogether  abandoned :  but  another  serious  evil  which 
would  then  be  experienced  prevents  this  substitution.  The 
glaze,  if  it  contained  beyond  a  certain  portion  of  alkali,  would 
not  undergo  the  same  degree  of  expansion  by  heat  as  the  body 
whereon  it  is  laid,  and  would,  as  a  consequence,  crack  to  such 
a  degree  as,  when  brought  into  use,  would  allow  any  greasy 


CHAP.  V. 


OF  FiRK  AND  GLAZING. 


67 


matter  to  penetrate  through  to  the  body  of  the  ware ;  and  this 
would  speedily  destroy  its  coherency. 

.  The  qualities  which  it  is  the  object  of  the  manufacturer  to 
give  to  porcelain  of  the  finest  description,  are  density,  white¬ 
ness,  transparency,  and  fine  texture  of  the  glaze.  These  prop¬ 
erties  are  estimated  in  the  order  wherein  they  are  here  enume¬ 
rated,  compactness  of  body  being  the  point  which  it  is  considered 
most  desirable  to  attain.  The  glaze,  as  seen  in  the  finished 
porcelain,  should  not  put  on  a  lustrous  appearance;  but  while 
beautifully  smooth  to  the  touch,  should  present  to  the  eye  rather 
the  softness  of  velvet  than  the  gloss  of  satin.  This  peculiar 
semblance  will  only  be  produced  with  glaze  that  melts  with 
difficulty,  and  when  the  heat  has  been  raised  precisely  to,  and 
not  beyond,  the  point  that  is  necessary  for  its  fusion. 

Stoneware  is  a  very  perfect  kind  of  pottery,  and  approaches 
nearer  than  any  other  description  to  the  character  of  porcelain. 
Its  body  is  exceedingly  dense  and  compact,  so  much  so,  indeed, 
that  although  vessels  formed  of  it  are  usually  glazed,  this  cov¬ 
ering  is  given  to  them  more  with  the  view  of  imparting  an  at¬ 
tractive  appearance  than  of  preserving  them  from  the  action  of 
liquids.  When  properly  made  and  baked,  stoneware  is  suffi¬ 
ciently  hard  to  strike  fire  from  flint,  and  is  as  durable  as  por¬ 
celain. 

This  kind  of  earthenware  is  composed  of  clay  and  flint.  The 
proportion  in  which  these  ingredients  are  used  is  said  to  vary 
in  different  manufactories,  and  it  is  difficult  to  ascertain  the 
precise  quantities  employed  in  any.  The  grinding  and  dilution 
of  the  materials  is  effected  in  the  manner  already  described, 
and  when  these  have  separately  been  thus  treated,  their  union 
is  commonly  effected  in  the  proportion  of  about  eighteen  mea¬ 
sures  of  argillaceous  to  fourteen  measures  of  siliceous  fluid. 
Any  larger  proportion  of  flint  would  render  the  compound  more 
lifficult  to  be  worked  ;  and  if  much  less  were  used,  the  baked 
svare  would  not  present  a  sufficiently  smooth  and  shining  ap- 
aearance. 

The  best  descriptions  of  this  ware  have  very  long  been  made 
n  the  potteries  at  Lambeth,  the  proprietors  of  which  procure 
heir  supply  of  clay  from  Devonshire  and  Dorsetshire,  and  pur- 
:hase  flint  already  ground  from  Staffordshire,  where  this  ma- 
erial  can  be  afforded  at  a  cheaper  rate  than  would  attend  its 
•reparation  so  near  the  metropolis. 

The  plan  introduced  by  the  two  brothers  Elers  is  still  pur- 
ued,  of  glazing  these  goods  by  the  decomposition  of  common 
alt  thrown  into  the  kiln,  at  or  near  the  conclusion  of  the  baking 
rocess.  Other  glazes  are  likewise  employed  for  many  articles, 
nd,  according  to  the  usual  system,  the  particular  components  of 


68 


PORCELAIN  MANUFACTURE. 


CHAP.  VI. 


these  are  also  veiled  in  mystery  ;  ground  glass  is,  however, 
understood  to  be  the  basis  of  all. 

One  of  the  most  considerable  of  the  Lambeth  potters  has  re¬ 
cently  announced  the  discovery  of  a  glazing  compound,  which 
is  sufficiently  fusible  without  containing  a  particle  of  lead,  and 
which  has  been  proved  capable  of  altogether  resisting  the  ac¬ 
tion  of  acids ;  it  is  used  by  him  for  coating  the  insides  of  jars 
and  bottles  of  all  descriptions. 

The  different  colors  observable  on  the  outer  surface  of  drink¬ 
ing  jugs  and  other  articles,  are  owing  to  the  partial  use  of  a 
glaze,  the  part  to  which  this  is  applied  becoming  dark  in  the 
heat,  of  the  kiln,  while  the  glazing  of  the  light  colored  portion 
is  caused,  as  before  mentioned,  by  the  introduction  of  salt. 

The  fashioning  of  stoneware  pottery  is  in  all  respects  con¬ 
ducted  similarly  to  the  processes  already  fully  described.  Seg- 
gars  are  mostly  employed  for  inclosing  the  pieces  during  the 
baking,  which  usually  occupies  about  forty-eight  hours. 

Vessels  of  considerable  size,  some  being  capable  of  containing 
sixty  imperial  gallons,  are  made  in  this  manner,  and  are  found 
highly  useful  in  performing  many  chemical  operations  con¬ 
nected  with  the  arts. 


CHAP.  VI. 

ON  THE  ART  OF  APPLYING  COLORS  AND  ENGRAVINGS  TO 
EARTHENWARE. 

Antiquity  of  Enamel  Coloring. — Specimens  from  Ancient  Egypt. — From  the 
Royal  Works  at  Sevres.-Painted  Ware  of  Worcester — Of  Staffordshire — 
Of  Derby — Of  Yorkshire. — Great  Services  of  Mr.  Wedgwood  in  this  Branch 
of  the  Manufacture. — Mystery  in  the  Preparation  of  Colors. — Publicatioh 
of  Processes  by  M.  Brongniart. — Metallic  Oxides — Addition  of  Fluxing 
Bodies  necessary — And  why. — Colors  Employed  for  tender  and  for  hard 
Porcelain. — Vehicle  used  with  the  Colors. — Mode  of  their  Combination. — 
Description  ofColors — Purple  and  Violet. — Red. — Yellow. — Blue. — Green. 
— Brown. — Black. — White. — Compound  Colors. — Precautions  necessary  in 
Forming  those  Compounds. — Gilding. — Lustreware. — Preparation  of  Col¬ 
ors. — Enamelling  Kilns. — Trial  Pieces. — Method  of  Gilding  and  Burnish¬ 
ing. — Copperplate  Engravings.- — Mode  of  Transferring  Impressions  to 
Earthenwares. — How  Performed  in  France. 

The  art  of  painting  on  earthenware,  although  of  compara¬ 
tively  recent  introduction  into  England,  is  by  no  means  a 
modern  invention.  It  is  well  known  that  the  ancients  manu¬ 
factured  colored  enamels ;  and  some  specimens  of  the  art,  per¬ 
formed  by  the  Egyptians  more  than  three  thousand  years  ago, 
have  been  preserved  to  the  present  day,  which  is  an  evidence 
of  this  fact;  showing  us,  at  the  same  time,  that,  in  so  remote  an 


CHAP.  VI.  APPLYING  COLORS  AND  ENGRAVINGS.  09 

age,  the  artists  of  Egypt  were  possessed  of  sufficient  practical 
knowledge  of  chemistry,  to  avail  themselves  of  processes  which 
have  been  brought  to  light  anew  by  scientific  investigators  of 
more  modern  times. 

Recently,  the  art  has  been  carried  to  an  admirable  degree  of 
perfection  in  Europe.  Some  specimens  are  preserved  in  the 
porcelain  works  at  Sevres,  of  which  the  French  artists  are 
justly  proud  ;  while  the  performances  in  our  own  potteries  at 
Worcester,  in  Staffordshire,  at  Derby,  and  yet  more  recently 
in  Yorkshire,  are  such  as  entitle  them  to  be  placed  in  an  equal 
rank  with  those  of  our  continental  neighbors. 

When,  about  seventy  years  ago,  Mr.  Wedgwood  commenced 
the  series  of  improvements,  by  which  his  name  has  been  ren¬ 
dered  so  deservedly  celebrated  throughout  Europe,  no  attempts 
at  embellishment  had  been  made  in  the  English  potteries ;  and 
if  ornamented  services  of  porcelain  were  seen  on  the  tables  of 
the  wealthy,  tney  were  always  of  foreign,  and  generally  of 
ariental  production.  So  soon,  however,  as,  by  the  intrinsic 
aierit  of  his  wares,  this  enterprising  manufacturer  had  secured 
lot  only  the  patronage  of  royalty,  but  the  more  solid  support  of 
lis  countrymen  in  general,  he  called  into  action  the  crucible  of 
:he  chemist,  and  the  pencil  of  the  artist,  and  led  the  way  in 
lestowing  that  degree  of  outward  embellishment  on  his  pro- 
luctions,  which  converted  them  into  objects  of  elegance,  and  at 
)nce  encouraged  and  gratified  the  growing  taste  for  luxury 
imong  the  higher  classes  in  this  country. 

The  system  of  mystery  still  preserved  in  the  English  pot- 
ories,  in  all  that  respects  the  composition  and  glazing  of  wares, 
vas  likewise  long  practised  with  regard  to  the  preparation  of 
:olors.  at  any  time,  a  manufacturer  had  found  out  a  prepa- 
ation  more  advantageous  than  that  in  use  before,  he  always 
mdeavored  to  limit  the  benefit  of  the  discovery  to  his  own 
vorks ;  a  desire  more  easy  of  accomplishment  formerly  than  it 
las  become  since  the  more  general  diffusion  of  the  light  of 
cience.  M.  Brongniart,  at  one  time  director  of  the  national 
oanufactory  of  porcelain  at  Sevres  in  France,  has  the  merit  of 
eing  the  first  who  published  a  correct  statement  of  the  most 
pproved  plans  for  preparing  and  combining  the  metallic  oxides 
sod  in  coloring  porcelain  and  glass.  The  employment  of  these 
abstances  for  such  purposes  had  been  long  before  and  com¬ 
ply  practised,  and  the  art  was  even  carried  by  some  of  its 
rofessors  to  a  high  degree  of  perfection ;  but,  as  M.  Brongniart 
isarves,  no  attempt  had  been  made  at  the  time  his  essay  was 
ritten  (1801),  to  apply  to  it  the  principles  of  chemical  science ; 
id  such  pretended  descriptions  as  had  then  been  published 
mtained  no  theory,  and  consequently  no  general  principles. 


70  PORCELAIN  MANUFACTURE.  CHAP.  VI. 

Where  even  the  authors  did  offer  explanations,  these  were 
founded  upon  the  most  ridiculous  hypotheses ;  so  that  all  im¬ 
provements  were  rather  the  offspring  of  chance  than  the  result 
of  systematic  inquiry. 

It  would  afford  but  little  satisfaction,  or  information,  to  relate 
by  what  steps  the  art  now  under  consideration  was  reduced 
into  a  system,  and  thus  became,  in  some  measure,  deserving  of 
the  name  of  a  science.  It  will  be  sufficient  to  state  the  means 
by  which  that  art  is  now  rendered  available  in  the  best  con¬ 
ducted  porcelain  works.  In  a  great  part  of  the  following  de¬ 
scription,  the  lucid  statements  given  by  M.  Brongniart  in  his 
essay  will  be  closely  followed  \  since,  with  scarcely  any  varia¬ 
tion,  the  same  processes  have  been  used  in  both  the  French 
and  English  establishments  to  the  present  day. 

In  this  branch  of  the  art  there  are  various  objects  to  be  con¬ 
sidered,  a  proper  acquaintance  with  which  is  necessary  to  suc¬ 
cess.  Such  are,  the  composition  of  colors ;  the  fluxes  which 
are  necessary  to  render  these  fusible,  which  unite  them  to  the 
wares,  and  in  many  cases  impart  brilliancy  to  their  tints ;  the 
vehicle  employed  in  laying  on  the  colors,  and  the  course  to  be 
pursued  in  fixing  them  on  "the  porcelain  by  means  of  heat. 

Metallic  oxides  form  the  bases  of  all  vitrifiable  colors,  but 
every  metallic  oxide  is  not  proper  for  being  employed  in  deco¬ 
rating  porcelain.  Some  are  highly  volatile,  as  the  oxides  of 
mercury  and  of  arsenic.  Others  part  so  freely  with  the  oxyger 
they  hold  in  combination,  that  their  color  proves  uncertain,  ant 
varies  with  every  application  of  heat  j  such  are  the  puce-coloret 
and  red  oxides  of  lead,  and  the  yellow  oxide  of  gold.  Oxides 
which  are  susceptible  of  great  variations  are  veiy  seldom  em 
ployed.  Black  oxide  of  iron  is  not  used  alone  for  producing 
that  color  on  porcelain  ;  and  the  green  oxide  of  copper,  as  for¬ 
merly  prepared,  was  so  uncertain  that  it  was  very  rarely  em 
ployed ;  but  this  evil  has,  since  the  time  of  M.  Brongniart 
been  greatly  remedied. 

Oxides  uncombined  with  other  substances  are  not  susceptibh 
of  fusion ;  and  although  they  may  be  attached  in  thin  strata  t< 
vitrifiable  bodies  by  a  very  violent  heat,  yet  their  colors,  witl 
the  exception  of  lead  and  bismuth,  would,  in  such  case,  becom< 
dull,  and  possibly  be  even  destroyed.  In  order  to  promote  thei 
fusion,  a  flux  is  therefore  added,  the  composition  of  which  vane 
according  to  the  means  employed  for  diluting  the  colors  at  th< 
time  they  are  used.  Where  a  volatile  oil  is  chosen  for  this  di 
lution,  a  flux  composed  of  glass,  nitre,  am],  borax  is  most  proper 
but  when,  as  in  the  Sevres  manufactory,  gum-water  is  substi 
tuted  for  this  volatile  oil,  the  flux  must  be  varied,  because  bora: 
cannot  be  properly  diluted  in  gum-water.  A  compound  of  glastj 


ClIAl*.  VI.  APPLYING  COLORS  A  AD  ENGRAVINGS.  71 

lead,  and  silex  is  therefore  preferred  by  M.  Brongniart,  who, 
however,  has  given  no  directions  regarding  the  proportions 
wherein  these  bodies  must  be  brought  together.  The  other 
menstruum,  which  is  recommended  by  M.  de  Montamy,  in  his 
treatise  on  painting  in  enamel,  is  composed  of 
Powdered  glass  40  parts. 

Calcined  borax  *  22 
Refined  nitre  -  44 

It  is  indispensable,  not  only  that  the  borax  and  nitre  be  as  pure 
as  they  can  be  rendered,  but  also  that  the  glass  shall  not  con¬ 
tain  the  smallest  particle  of  lead  in  its  composition.  These  in¬ 
gredients  must  first  be  well  triturated  together  in  a  glass  mor¬ 
tar,  with  a  pestle  of  the  same  material,  during  an  hour,  and 
then  exposed  in  a  crucible  to  the  heat  of  a  charcoal  fire,  until 
the  swelling,  which  for  a  time  accompanies  the  fusion  of  the 
mass,  has  ceased. 

By  means  of  this  flux  the  colors  are  fixed  upon  the  porce¬ 
lain,  and  made  to  assume  a  resplendent  appearance :  the  metallic 
oxides,  being  enveloped  by  the  flux,  are  preserved  from  all  con¬ 
tact  with  the  air,  and  their  color  is  rendered  permanent ;  the 
fusion  having  been  promoted  at  a  temperature  too  low  for  their 
destruction. 

Trial  should  be  made  of  the  habitudes  of  different  colors  in 
combination  with  their  flux,  in  order  to  determine  the  exact 
quantity  to  be  employed  with  each.  Various  substances  vitrify 
with  greater  or  less  facility  when  thus  combined,  and  the 
greatest  carefulness  and  skill  are  consequently  required,  so  to 
proportion  the  relative  quantities  of  each,  that  not  more  of  the 
flux  shall  be  added  than  is  necessary  to  cause  a  perfect  vitrifi¬ 
cation.  If  too  little  were  used,  the  colors,  although  they  might 
attach  themselves  to  the  porcelain,  would  nevertheless  be  dull ; 
and  if  too  much,  the  colors  would  run,  their  outlines  would  not 
be  sufficiently  decided,  and  all  the  finer  touches  of  the  artist 
would  disappear.  It  has  been  remarked,  that  colors  which  re¬ 
quire  for  their  fusion  more  than  six  times  their  weight  of  flux, 
do  not  flow  with  sufficient  facility  ;  and,  as  they  cannot  be  ap¬ 
plied  with  a  pencil,  so  as  to  produce  a  satisfactory  result,  should 
be  rejected. 

Such  metallic  oxides  as  would  have  their  colors  altered  by  a 
strong  or  often  repeated  heat,  are  employed  after  being  mixed 
with  their  flux,  but  without  having  been  previously  fused  with 
it.  In  many  cases  metallic  oxides  are  first  fused  with  the 
requisite  proportion  of  their  flux,  and  are  then  ground  for  use. 

*  Mr.  Tillnch  remarks  (Philos.  Mag.  vol.  li.)  that  borax  should  be  used 
sparingly,  as  it  causes  efflorescence,  and  promotes  the  decay  of  the  enamel 


72 


PORCELAIN  MANUFACTURE. 


CHAP.  VI. 


Enamel  is  glass  made  opaque  by  the  oxide  of  tin,  and  ren¬ 
dered  fusible  by  the  oxide  of  lead.  All  glazes  that  contain  lead 
participate  in  the  properties  of  enamel.  Raw  glazes  used  for 
covering  tender  porcelain  are  of  this  nature.  The  colors  em¬ 
ployed  in  painting  this  porcelain  are  those  which  serve  for 
painting  in  enamel ;  they  require  less  flux  than  others,  because 
the  surface  to  which  they  are  applied  becomes  soft  enough  to 
be  penetrated  by  them.  Hard  porcelain,  whose  nature  is  iden¬ 
tical  with  those  of  China  and  Saxony,  has  two  kinds  of  colors 
applied  to  it.  Those  of  the  first  kind,  which  are  used  in  the 
representation  of  different  objects,  are  baked  in  a  heat  much 
below  that  necessary  for  baking  porcelain ;  while  the  other 
colors,  which  are  few  in  number,  must  be  exposed  to  the  highest 
degree  required  by  the  porcelain  itself.  The  glaze  used  for 
hard  porcelain  has  little  or  no  lead  in  its  composition.  The 
Sevres  manufacturers,  and  some  few  in  England,  employ  fel¬ 
spar  without  any  mixture  of  lead.  This  glaze,  when  exposed 
to  the  heat  of  the  gloss  oven,  dilates,  and  its  pores  are  opened 
without  becoming  soft,  so  that  the  colors  are  not  absorbed  by  it, 
and  do  not  undergo  those  changes  which  occur  when  they  are 
applied  to  tender  porcelain,  where,  by  mixing  with  the  body  of 
the  enamel,  they  become  faint  and  indistinct.  This  effect  is 
much  increased  likewise  where  some  particular  colors  are  em¬ 
ployed,  and  especially  the  reds  produced  from  iron,  which  are 
exposed  to  the  destructive  action  of  the  oxide  of  lead  that  is 
contained  in  the  glaze.  Painting  on  tender  porcelain  must,  for 
these  reasons,  be  several  times  retouched  with  the  pencil,  in 
order  to  give  to  it  the  distinctness  and  brilliancy  which  follow 
the  use  of  the  same  colors  on  hard  porcelain,  so  that  a  high  de¬ 
gree  of  ornament  is  seldom  or  never  given  to  any  but  the  latter 
description.  In  the  embellishment  of  hard  porcelain,  these  re¬ 
touchings  are  not  required,  except  for  the  most  elaborate  speci¬ 
mens  of  the  art,  which  can  by  such  means,  however,  be  pro¬ 
duced  with  the  most  admirable  degree  of  perfection,  so  as  to 
render  paintings  on  porcelain  not  distinguishable  from  the 
finest  productions  of  the  pictorial  art,  without  reference  to  the 
body  upon  which  it  is  performed,  or  to  the  means  used  for 
bringing  out  the  colors ;  natural  objects,  landscapes,  portraits, 
and  even  historical  pieces  being  represented  with  all  the  truth, 
as  well  as  with  all  the  brilliancy  of  coloring,  which  distinguish 
the  works  of  the  first  masters. 

One  great  inconvenience  attends  the  repeated  exposure  to 
the  heat  of  the  oven  of  pieces  thus  retouched ;  the  colors  being 
liable  to  peel  off*,  unless  the  greatest  care  has  been  used  in  their 
application.  This  defect  has  been  remedied  in  the  Sevres 
works,  by  introducing  a  calcareous  flux  into  the  felspar  glaze, 


73 


CHAP.  VI.  APPLYING  COLORS  AND  ENGRAVINGS. 

which  soflens  it,  without  at  all  affecting  the  body  of  the  ware. 
Soda  and  potash  are  never  used  as  fluxes,  as  their  introduction 
causes  the  colors  to  scale ;  the  reason  for  which  is,  that,  becom¬ 
ing  volatile  in  a  great  heat,  they  abandon  the  color,  which  then 
will  not  adhere  to  the  glaze. 

The  liquid  matter  which  serves  as  a  vehicle  in  laying  on  the 
colors,  is  rubbed  with  them  upon  a  glass  palette  until  the  whole 
is  intimately  united.  The  mixture  must  be  brought  to  that 
state  of  dilution  which  is  most  proper  and  convenient  for  its 
application  with  a  hair  pencil  on  the  surface  of  the  porcelain. 
Great  care  is  used  in  the  choice  and  management  of  these  dilu¬ 
ent  liquids,  which  must  always  be  sufficiently  volatile  to  be  en¬ 
tirely  dissipated  in  the  heat  to  which  the  wares  are  afterwards 
exposed.  In  France,  the  preference  is  given  to  oil  of  lavender 
as  a  vehicle ;  and  in  order  to  insure  the  proper  degree  of  fluid¬ 
ity,  this  oil  is  divided  by  distillation  into  two  parts :  that  which 
first  comes  over,  being  the  most  volatile,  and  having  the  least 
density,  is  used  for  diluting  the  colors  when  they  become  too 
thick ;  and,  on  the  other  hand,  the  portion  that  remains  in  the 
retort,  having  the  opposite  qualities,  is  reserved  for  thickening 
them  when  they  run  too  freely.  Oil  of  turpentine,  which  has 
been  some  time  in  store,  is  more  generally  used  in  England, 
and  is  said  to  answer  the  purpose  better  than  any  other  volatile 
fluid. 

It  was  remarked  by  Brongniart,  whose  practical  knowledge 
qualified  him  to  judge  correctly  on  the  subject,  that  of  all  the 
processes  for  painting  on  glass  and  porcelain  described  in  works 
that  were  in  existence  at  the  time  his  essay  was  published, 
there  was  not  one,  by  strictly  following  which,  the  desired  co¬ 
lors  could  be  produced.  In  describing  these  processes,  one  au¬ 
thor  had  followed  another  without  knowledge  or  examination ; 
and  even  the  treatise  by  Leviel,  which  forms  part  of  the  volu¬ 
minous  work  on  arts  and  manufactures,  published  under  the 
auspices  of  the  Academy  of  Sciences  in  Paris,  is  not  free  from 
this  reproach.  Such  want  of  correctness,  from  whatever  cause 
it  may  have  arisen,  is  little  honorable  to  the  authors,  who  if 
even  unable,  by  penetrating  the  veil  of  mystery  wherein  the 
manufacturers  shrouded  their  practices,  to  expose  them  correct¬ 
ly  to  the  world,  might,  without  difficulty,  have  ascertained  the 
truth  or  falsehood  of  that  to  which  they  were  affixing  the  stamp 
of  their  authority.  The  course  which  they  pursued  would  as¬ 
suredly  fail  of  success  in  the  present  day,  when  an  acquaintance 
with  chemical  phenomena  is  no  longer  confined,  as  it  formerly 
was,  to  a  few  among  the  rarer  order  of  students,  and  such  er¬ 
rors  would  be  certain  of  confutation  at  the  moment  of  their  pro¬ 
mulgation. 


74 


PORCELAIN  MANUFACTURE. 


CHAP.  VI. 


Purple  and  violet  colors  are  procured  by  dissolving  gold  in 
aqua  regia  (nitro-muriatic  acid),  and  immersing  a  bar  of  pure  tin 
in  the  solution.  The  product  thus  obtained  is  called,  from  its  in¬ 
ventor,  the  purple  precipitate  of  Cassius,  and  is  used  very  gen¬ 
erally  for  giving  the  above-mentioned  colors  to  porcelain.  A 
preferable  way  of  preparing  this  precipitate  is  to  dissolve  the 
two  metals  separately,  and  by  then  bringing  the  solutions  to¬ 
gether  in  different  proportions,  various  shades  of  carmine,  vio¬ 
let,  and  purple  are  obtained.  The  first  of  these  three  tints  is 
seldom  used  in  porcelain  works,  for  although  extremely  beauti¬ 
ful,  it  is  also  very  transient,  and  may  be  easily  spoilt  by  a  small 
excess  of  heat,  or  by  the  contact  of  carbonaceous  vapors,  a  cir¬ 
cumstance  which  is  the  less  important,  as  its  place  may  be  well 
supplied  by  a  rose  color  obtained  from  iron,  and  which  is  not 
liable  to  the  same  disadvantage.  Carmine  color,  when  used  for 
tender  porcelain,  is  prepared  with  fulminating  gold  (made  by 
dissolving  the  metal  with  aqua  regia  and  precipitating  with  am¬ 
monia),  and  muriate  of  silver.  This  compound  is  without  any 
addition  of  tin,  which  shows  that  an  union  of  the  oxide  of  tin 
with  that  of  gold  is  not  necessary — as  many  have  supposed — 
for  the  production  of  purple. 

Violet  color  is  also  made  with  the  purple  oxide  of  gold,  re¬ 
quiring  the  presence  of  some  portion  of  lead  in  the  flux  for  the 
development  of  this  shade.  These  three  colors  cannot  bear 
exposure  to  the  full  heat  of  a  porcelain  furnace,  in  which  they 
would  wholly  disappear.  In  using  the  precipitate  of  gold,  it  is 
mixed  with  about  six  times  its  own  weight  of  flux,  and  is  em¬ 
ployed  without  previously  fusing  the  two  bodies  together. 
When  first  applied  on  the  porcelain,  it  is  of  a  dirty  violet  color, 
but  by  exposure  to  heat  this  passes  to  a  most  beautiful  purple. 
It  is  recommended  to  employ  charcoal  as  fuel  in  baking  this 
color.  Frequent  exposure  to  the  fire  will  materially  impair  its 
beauty. 

Red  oxide  of  iron,  prepared  by  the  united  action  of  fire  and 
nitric  acid  (the  aquafortis  of  commerce)  yields  a  red  color, 
which,  although  beautiful,  is  less  brilliant  than  that  produced 
from  gold.  As  already  stated,  it  is,  however,  preferable  on  ac¬ 
count  of  its  less  liability  to  change.  Shades  of  red,  deepening 
from  rose  color,  and  passing  by  the  increased  application  of 
heat  to  brown,  are  obtained  from  iron.  The  flux  employed  with 
this  oxide  is  composed  of  vitrified  borax,  sand,  and  a  small  pro¬ 
portion  of  red  lead,  and  the  color  may  be  used  either  with  or 
without  previous  fusion  with  its  flux.  By  the  mixture  of  black 
and  red  oxides  of  iron,  in  different  proportions,  various  shades 
of  reddish  brown,  chestnut,  &c.  are  obtained.  Red  colors  pro¬ 
duced  from  iron  cannot  be  used  on  tender  porcelain,  since  they 


CHAP.  VI.  APPLYING  COLORS  AND  ENGRAVINGS. 


75 


disappear,  in  that  case,  on  exposure  to  heat.  This  effect  must 
be  ascribed  to  the  presence  of  lead  in  the  glaze.  Several  ex¬ 
periments,  conducted  by  M.  Brongniart,  have  proved  this  fact 
beyond  all  controversy. 

A  very  permanent  red  color  is  procured  by  calcining  the  ox¬ 
ide  of  iron  with  double  its  own  weight  of  common  salt  (chlo¬ 
ride  of  sodium).  The  processes  used  for  this  purpose  must  be 
carefully  conducted,  and  the  salt  purified  and  decrepitated — 
that  is,  subjected  to  the  action  of  heat  until  all  crackling 
noise  has  ceased.  The  oxide  is  procured  by  dissolving  iron 
filings  in  nitric  acid,  and  precipitating  with  salt  of  tartar  (sub¬ 
carbonate  of  potass).  The  precipitate  must  then  be  placed  on 
a  thin  sheet  of  iron,  and  exposed  under  a  muffle  to  the  heat  of 
a  charcoal  fire,  until  it  has  taken  a  fine  red  color.  The  two 
substances  having  been  well  triturated  together  in  a  glass  or 
porcelain  mortar,  are  then  calcined  in  a  crucible,  and  the  oper¬ 
ation  should  be  carried  as  far  as  possible,  without  occasioning 
the  vitrification  of  the  mass.  When  taken  from  the  fire  and 
cooled,  the  compound  is  again  triturated ;  successive  portions 
of  hot  water  are  poured  upon  it,  stirred,  and  then  removed, 
until  the  water  is  no  longer  colored.  The  fluid  thus  tinged 
is  allowed  to  settle,  and  is,  when  clear,  poured  from  the  sedi¬ 
ment,  which  is  then  washed  five  or  six  times  in  fresh  portions 
of  clear  water. 

To  obtain  yellow  colors,  for  both  hard  and  tender  porcelain, 
white  oxide  of  antimony,  mixed  with  sand  and  oxide  of  lead, 
are  employed,  the  latter  substance  serving  as  a  flux  to  the 
others.  Great  carefulness  is  required  in  the  preparation,  as  the 
lead  frequently  approaches,  by  reason  of  the  heat,  to  a  metallic 
6tate,  and,  in  that  case,  appears  in  the  form  of  black  spots  on 
the  wares.  Oxide  of  tin  is  sometimes  added,  and  when  the  co¬ 
lor  is  required  to  be  livelier,  and  approaching  to  that  of  saffron, 
red  oxide  of  iron  is  added,  the  too  great  redness  of  this  being 
subdued  by  the  action  of  the  lead,  in  the  fusion  which  the  ingre¬ 
dients  undergo,  previous  to  their  application  on  the  porcelain. 
The  colors  thus  produced  are  not  susceptible  of  change,  but  if 
exposed  to  the  full  heat  of  a  porcelain  furnace  would  be  en¬ 
tirely  dissipated. 

Oxide  of  uranium,  mixed  with  oxide  of  lead,  produces  a 
straw  color.  By  decomposing  chromate  of  potass,  with  nitrate 
of  lead,  which  is  a  saturated  solution  of  lead  in  nitric  acid,  chro¬ 
mate  of  lead  is  precipitated,  and  this  proves  a  very  excellent 
yellow  color. 

Naples  yellow  is  composed  of  24  parts  of  ceruse,  4  parts  of 
oxide  of  antimony,  and  one  part  each  of  alum  and  sal  ammoniac 
(muriate  of  ammonia),  calcined  together  at  a  moderate  heat 


76 


PORCELAIN  MANUFACTURE. 


CHAP.  VI. 


during  three  hours.  The  shade  is  varied  by  increasing  or  di¬ 
minishing  the  proportion  of  sal  ammoniac.  The  quantity  of  flux 
that  must  be  combined  with  this  color  for  use  is  uncertain,  and 
must  be  matter  for  experiment  with  the  manufacturer. 

For  the  production  of  blue,  well  prepared  and  very  pure 
oxide  of  cobalt  is  employed,  mixed  with  a  flux.  Oxides  of  tin 
and  of  zinc,  added  in  different  proportions,  give  different 
shades,  from  a  deep  rich  color  to  a  light  blue.  As  the  oxide  of 
cobalt  is  volatilized  at  a  high  heat,  it  is  impossible  to  place  in 
the  same  case,  white  pieces,  and  such  as  are  painted  blue ; 
since  the  former  would  certainly  assume  a  bluish  tint  in  the 
operation  of  baking.  This  difficulty  does  not  occur  with  tender 
porcelain,  on  which  the  cobalt  is  not  volatilized  as  in  the  other 
case,  owing  to  the  heat  being  very  inferior  to  that  used  in  ba¬ 
king  hard  porcelain.  These  blue  colors,  if  they  have  been  pre¬ 
viously  fused,  do  not  change  at  all  after  their  application.  The 
rich  smalt,  known  under  the  name  of  azure-blue,  is  only  the 
glass  of  cobalt,  mixed  with  sand.  This  color  must  be  fused  in 
a  crucible,  and  reduced  to  an  impalpable  powder  in  an  agate 
mortar,  after  which  it  may  be  used  in  combination  with  flux. 

Prussian  blue,  which  results  from  the  union  of  hydrocyanic 
acid  with  oxide  of  iron,  is  very  extensively  used  in  the  arts; 
and  being  prepared  on  a  large  scale  for  sale,  in  various  parts  of 
the  kingdom,  no  manufacturer  of  porcelain  will  undergo  the 
trouble,  or  encounter  the  unpleasant  circumstances  attendant 
upon  its  preparation,  but  will  rather  obtain  the  comparatively 
small  quantity  he  may  require  by  purchase. 

Green  oxide  of  copper  is  usually  employed  for  the  production 
of  a  green  color.  On  precipitating  in  different  vessels,  by  means 
of  potass,  solutions  of  copper  which  are  equally  pure  and  con¬ 
centrated,  it  is  perceptible  that  the  precipitate  is  formed  more 
quickly  in  some  vessels  than  in  others;  and  if  these  different 
products  are  separately  collected,  those  which  are  most  prompt¬ 
ly  formed  are,  when  dried,  of  a  fine  bright  green,  and  produce 
a  corresponding  color  on  porcelain ;  while  those  precipitates 
which  are  deposited  more  slowly,  form  earthy  and  less  dense 
particles  of  a  much  darker  hue,  and  which,  when  applied  to  por¬ 
celain,  yield  a  less  pleasing  color,  and  pass  sometimes  to  black 
during  the  baking.  If,  however,  the  precipitated  oxide  is  pre¬ 
viously  fused  with  its  flux,  this  change  need  not  be  apprehend¬ 
ed.  Very  pure  oxide  of  copper  is  frequently  procured  by  pla¬ 
cing  sheets  of  the  metal  in  the  oven  wherein  the  ware  is  glazed. 
Mixtures  of  yellow  and  blue  are  sometimes  used  in  the  compo¬ 
sition  of  green  colors :  some  of  these  will  not  exist  in  the  heat 
of  a  porcelain  furnace.  Various  shades  of  beautiful  green  may 
be  obtained,  by  mixing,  in  different  proportions,  Prussian  blue 


CHAP.  VI.  APPLYING  COLORS  AND  ENGRAVINGS.  77 

with  the  chromate  of  lead  already  described.  A  mixture  of  the 
oxides  of  cobalt  and  nickel,  will  resist  a  very  intense  heat,  but 
does  not  produce  a  genuine  green :  it  is  rather  an  olive  color. 

Oxide  of  chromium  gives  a  beautiful  green  color,  which  is 
indestructible  in  the  heat  of  a  porcelain  furnace.  That  class  of 
green  colors,  called  celestial  blues,  can  only  be  applied,  accord¬ 
ing  to  Brongniart,  on  tender  wares :  being  partly  composed  of 
potass,  they  scale  off  from  hard  porcelain. 

Different  shades  of  light  and  of  deep  rich  brown  are  obtained 
from  mixtures  of  the  oxides  of  iron.  These  must  be  fused 
with  thin  flux  before  they  are  used,  after  which  fusion  they  do 
not  undergo  any  change  on  the  application  of  heat.  Russet 
grounds,  known  under  the  designation  of  tortoise-shell,  are  pro¬ 
duced  in  this  manner.  Felspar  is  employed  as  a  flux  with  these 
colors. 

There  is  not  any  metallic  oxide  which  alone  will  give  a  good 
black.  Oxide  of  manganese  approaches  the  nearest  to  it.  The 
black  oxide  of  iron  yields  a  very  dull  color,  which  sometimes 
changes  to  red.  The  color-makers  therefore  unite  several  ox¬ 
ides  together,  and  thence  obtain  a  very  beautiful  black.  The 
oxides  thus  combined  are  of  manganese,  the  brown  oxide  of 
copper,  and  a  small  proportion  of  the  oxide  of  cobalt.  A  gray 
color  is  obtained  by  omitting  the  copper,  and  increasing  the 
proportionate  quantity  of  the  flux. 

Cobalt,  oxide  of  copper,  and  umber,  in  equal  parts,  reduced 
together  to  an  impalpable  powder  in  an  agate  mortar,  prove  a 
very  good  black.  This  must  be  used  with  three  times  its 
weight  of  flux.  Another  black  is  composed  of  four  parts  oxide 
of  copper,  one  part  of  smalt,  and  one  part  of  black  oxide  of  iron, 
which,  like  the  former  compound,  must  be  rubbed  together  to  a 
fine  powder,  and  used  with  three  parts  of  flux. 

In  the  “  Annales  de  Chimie  et  de  Physique,”  (Yol.  20. 1822), 
directions  are  given  for  the  preparation  of  a  beautiful  black  en¬ 
amel,  the  verification  of  which  on  the  part  of  our  porcelain 
manufacturers  is  perhaps  desirable.  The  experiment  necessary 
for  this  purpose  might  have  been  somewhat  simplified,  if  the 
artist  by  whom  the  directions  are  communicated  had  stated  the 
proportions  wherein  the  ingredients  should  be  brought  together. 
The  formula  directs  that  chloride  of  platina,  dissolved  in  water, 
should  be  mixed  with  nitrate  of  mercury.  By  then  subjecting 
the  precipitate  which  will  be  formed  to  a  heat  just  sufficient  to 
volatilize  the  proto- chloride  of  mercury,  a  black  powder  will  be 
obtained.  This  is  the  enamel,  which  must  be  applied  in  the 
usual  manner,  in  combination  with  a  fluxing  material. 

M.  de  Montamy  in  his  treatise,  to  which  allusion  has  already 
been  made,  gives  a  recipe  for  composing  a  pure  white  color, 

G  2 


78 


PORCELAIN  MANUFACTURE. 


CHAP.  VI. 


which  is  found  very  serviceable  by  the  French  artists  in  form¬ 
ing  their  series  of  shades,  as  well  as  in  the  composition  of  those 
parts  of  their  designs  which  require  to  be  represented  in  a  bril¬ 
liant  white.  This  color  is  composed  of  one  part  of  virgin  tin, 
and  two  parts  of  common  salt.  The  latter  must  be  thoroughly 
purified,  by  first  dissolving  it  in  distilled  water,  then  filtering 
the  solution  through  paper,  and  afterwards  evaporating  it  to 
dryness  over  the  fire  in  a  porcelain  capsule.  The  salt,  which  is, 
by  this  means,  made  extremely  white,  must  be  further  exposed 
to  heat  in  a  crucible,  until  all  decrepitating  noise  has  ceased. 
The  purification  will  be  yet  more  perfect,  if,  after  filtering  it, 
the  solution  is  partially  evaporated,  and  then  placed  in  a  cool 
situation  to  crystallize  slowly.  Those  artists  who  are  the  most 
particular  in  their  processes,  select  preferably  from  the  rest 
such  crystals  as  take  the  form  of  cubes.  The  next  part  of  the 
process  is  to  place  a  crucible  on  the  fire,  well  covered,  to  pre¬ 
vent  the  entrance  of  smoke  or  ashes.  When  this  crucible  is  at 
a  red  heat,  the  tin  is  introduced,  and  is  left  until  it  is  not  only 
fused,  but  red-hot,  at  which  time  the  purified  salt  is  added  in 
the  proportion  already  mentioned.  Taking  then  a  clean  iron 
spatula,  the  end  of  which  must  be  previously  heated,  the  mix¬ 
ture  is  stirred  until  the  substances  are  well  incorporated  to¬ 
gether.  The  crucible  being  then  again  covered,  is  to  be  sur¬ 
rounded  with  burning  charcoal,  and  from  time  to  time,  the 
spatula,  which  must  be  always  perfectly  clean  aud  hot,  should 
be  introduced  to  agitate  the  mass.  When  the  end  of  this  spat¬ 
ula,  in  being  tempered  by  the  heat  of  the  crucible,  begins  to  grow 
white,  it  is  a  sign  that  the  calcination  is  carried  sufficiently  far, 
and  that  the  crucible  should  be  removed  from  the  fire ;  the  cal¬ 
cination  usually  occupies  an  hour  for  its  completion.  The  com¬ 
pound  should  next  be  bruised  in  a  mortar  of  glass  or  of  agate, 
and  again  placed  in  a  crucible  which  is  set  in  the  midst  of 
burning  coals  and  covered  with  a  muffle.  The  heat  is  then 
raised  gradually,  and  continued  during  three  hours,  when,  on 
removing  the  crucible  from  the  fire,  the  color  is  found  to  be 
hard,  and  requires  some  force  to  detach  it  from  the  vessel. 
This  done,  it  must  be  pounded  in  a  mortar,  and  washed  in  hot 
water  that  has  been  filtered  or  distilled,  and  fresh  portions  of 
water  added,  until  the  fluid  has  no  longer  any  taste  of  salt. 
The  white  color  is  afterwards  to  be  boiled  violently  with  an 
abundance  of  water  in  an  earthenware  vessel  for  two  hours, 
supplying  hot  water  during  that  time  to  replace  the  portion  that 
is  evaporated.  When  the  supernatant  water  has  become  clear 
by  standing,  it  must  be  poured  off  carefully. 

This  white  may  be  advantageously  employed  in  painting  with 
oil,  as  it  mixes  well  with  it.  When  used  on  porcelain,  it  must 


CHAP.  VI.  APPLYING  COLORS  AND  ENGRAVINGS.  79 

be  mixed  with  three  times  its  weight  of  flux.  The  preparation 
of  this  color  will  not  succeed  unless  the  tin  is  extremely  pure, 
and  it  is  essential  that  the  nicest  possible  degree  of  cleanliness 
should  be  observed  throughout  the  operations. 

By  making  different  mixtures  of  the  various  colors  here  de¬ 
scribed,  every  hue  that  can  be  desired  may  be  obtained.  It  is 
not,  however,  so  easy,  as  without  due  consideration  it  might 
appear,  to  produce  these  various  shades.  Great  judgment  in 
the  selection  of  materials,  carefulness  in  their  preparation,  and 
knowledge  as  to  the  relative  proportions  wherein  they  should  be 
brought  together,  are  essential  to  success;  and  an  acquaintance 
with  the  science  of  chemistry  is  highly  desirable.  There  are 
some  colors  which,  if  mixed,  would  mutually  destroy  each  other, 
and  on  the  exposure  of  metallic  oxides  to  heat,  changes  ensue, 
which  result  not  from  the  nature  and  habitudes  of  the  colors 
themselves,  but  rather  from  the  influence  of  the  bodies  to  which 
they  are  applied. 

.  It  would  be  scarcely  possible  to  treat  satisfactorily  upon  the 
inciting  causes  of  all  these  variations,  a  full  knowledge  of  which 
can  result  alone  from  the  practical  experience  of  the  artist  and 
manufacturer. 

Many  potters  do  not  prepare  their  own  enamel  colors,  but 
purchase  what  they  require  from  persons  who  manufacture  them 
for  sale.  Some  of  these  preparations  are  exceeding  costly,  and 
as  the  temptation  to  adulterate  them  is  consequently  great,  the 
potter  should  have  good  reason  to  rely  on  the  probity  of  the 
color-maker  with  whom  he  deals.  A  fraudulent  mixture,  the 
detection  of  which  would  be  impossible  before  its  use,  except 
by  means  of  a  chemical  analysis,  might  be  the  occasion,  in  its 
results,  of  severe  loss  and  disappointment.  With  the  exception 
of  the  great  works  at  Sevres,  this  system  of  purchasing  their 
enamel  colors  has,  for  many  years  past,  been  very  general  among 
the  potters  of  France.  In  a  report  made  to  the  French  govern¬ 
ment,  by  a  commission  appointed  in  1819,  to  examine  into  the 
progress  of  manufacturing  industry  in  that  country,  occasion 
was  taken  for  offering  congratulations  upon  this  establishment 
of  an  independent  occupation,  as  marking  the  great  extension 
of  the  porcelain  manufacture,  and  as  offering  to  the  artist 
Deans  of  obtaining  every  shade  of  color,  prepared  by  persons 
vhose  interest  is  involved  in  ascertaining  their  effects  when 
submitted  to  the  heat  of  the  furnace,  thus  removing  all  uncer- 
ainty  from  the  operations  of  the  painter,  and  rendering  it  un- 
lecessary  for  him  to  suspend  his  work  that  he  may  prepare  his 
solors. 

The  gold  used  in  gilding  porcelain  is  applied  in  a  metallic 
tate.  To  prepare  it  for  this  purpose,  it  is  dissolved  in  aqua 


80 


Porcelain  manufacture. 


chap.  VI. 


regia,  and  the  acid  being  afterwards  dissipated  by  the  applica¬ 
tion  of  heat,  the  gold  remains  in  the  state  of  powder  at  the  bot¬ 
tom  of  the  vessel.  This  powder  must  be  mixed  with  borax 
and  gum-water,  as  a  vehicle  for  causing  it  to  flow  from  the 
pencil  and  fix  upon  the  wares;  which  being  then  baked,  the 
gilding  appears  void  of  lustre,  and  requires  to  be  afterwards 
burnished  with  either  agate  or  blood-stone. 

Gold  and  silver  lustre-ware  is  commonly  of  an  inferior  quality. 
The  metallic  oxides  used  for  covering  these  vessels  are  inti¬ 
mately  mixed  with  some  essential  oil,  and  then  brushed  entirely 
over  their  surfaces.  The  heat  of  the  enamelling  oven,  which 
dissipates  the  oxygen,  restores  the  oxides  to  their  metallic  state, 
but  with  some  diminution  of  brilliancy.  The  oxide  of  plati¬ 
num  is  used  for  making  silver-lustre. 

Colors,  when  they  are  required  for  use,  should  be  first 
pounded  quickly  in  a  mortar  made  of  either  agate,  porcelain,  or 
glass,  with  a  pestle  of  the  same  material,  and  covered  to  pre¬ 
vent  the  access  of  dust.  They  must  be  afterwards  ground  on  a 
glazed  palette,  firmly  bedded  in  plaster  on  a  wooden  frame,  and 
perfectly  level.  The  artist  who  decorates  porcelain  is  required 
to  rub  his  colors  with  as  much  nicety  as  is  used  by  miniature 
painters,  so  that  there  must  not  remain  the  least  perceptible 
roughness,  either  under  the  muller  or  between  the  fingers.  The 
requisite  proportions  of  volatile  oil  and  of  flux  are  added  and 
ground  with  the  colors  on  the  palette,  the  whole  having  been 
carefully  weighed  before  their  union.  The  general  rule  is  to 
put  five  parts  of  flux  to  two  parts  of  coloring  matter :  but  some 
colors,  as  already  mentioned,  require  more,  while  with  others 
this  proportion  would  be  too  great.  Smalt  requires  to  have 
combined  with  it  only  half  the  sum  of  its  own  weight. 

The  artist  must  be  attentive  to  grind  his  colors  with  the 
smallest  quantity  of  oil  that  will  suffice ;  if  this  should  be  in  ex¬ 
cess,  it  may  in  evaporating  leave  spaces  between  the  particles 
of  color,  and  the  subject  would  appear  very  imperfectly  exe¬ 
cuted.  The  fluidity  of  the  mixture  should  be  kept  at  that  ex¬ 
act  point  which  enables  the  artist  to  produce  the  finest  strokes 
with  clearness  and  facility. 

Before  the  pieces  which  have  been  painted  are  baked  in  the 
enamelling-kiln,  it  is  necessary  to  dry  the  colors  by  evaporating 
the  oil  used  with  them  as  the  vehicle. 

Every  considerable  pottery  has  enamelling-kilns  of  various 
sizes.  These  are  in  form  like  a  chemist’s  muffle,  from  about 
six  to  ten  feet  long,  and  from  three  to  five  feet  wide.  The  ar¬ 
ticles  are  piled  in  the  kiln  until  it  is  filled,  when  the  mouth  be¬ 
ing  closed,  fire  is  applied,  and  continued  for  about  eight  or  ten 
hours,  at  the  end  of  which  time  the  colors  are  found  to  be  burnt 


CHAP.  VI.  APPLYING  COLORS  AND  ENGRAVINGS.  81 

into  the  glaze.  In  piling  the  pieces  in  the  kiln,  care  must  be 
used  to  avoid  the  placing  of  any  one  piece  upon  the  gilt  border 
of  another.  The  muffle  is  provided  with  trial  pieces,  which 
can  be  extracted  from  time  to  time  during  the  baking,  and 
which  will  indicate  the  general  state  of  the  contents  of  the  kiln, 
so  as  to  govern  the  continuance  of  the  operation.  No  delay 
should  occur  between  the  sufficient  baking  of  the  colors,  and 
the  withdrawing  of  the  fire,  as  their  brilliancy  would  be  injured 
by  its  longer  continuance.  The  contents  of  the  kiln  are  left 
undisturbed  until  they  are  cool,  and  are  then  withdrawn.  All 
impure  exhalations  are  prejudicial  to  the  beauty  of  colors,  and 
every  substance  whence  they  can  arise  should,  as  far  as  possi¬ 
ble,  be  kept  away  from  the  kiln  during  the  process. 

Gilding  on  porcelain  or  on  glass  is  performed  either  with  or 
without  the  addition  of  a  fluxing  material,  the  gold  being  made 
to  adhere  to  the  surface  by  the  incipient  fusion  of  either  the 
glazing  on  the  porcelain,  or  of  the  surface  of  the  glass,  or  of  the 
flux  employed. 

Gold  is  used  for  this  purpose  sometimes  in  the  form  of  leaf 
gold,  and  at  other  times  in  that  of  powder,  prepared  either  me¬ 
chanically,  or  by  chemical  precipitation.  When  the  first  of 
these  two  methods  is  employed,  leaf  gold  must  be  ground  with 
honey  or  with  gum-water  of  an  equal  consistence ;  the  honey 
or  gum  being  afterwards  washed  away,  the  gold  may  be  kept 
for  use  in  paper  or  in  shells,  and  the  use  of  these  latter  recipi¬ 
ents  has  occasioned  this  powder  to  be  known  among  artists  as 
“  shell  gold.”  This  precious  metal  is  precipitated  from  its  solu¬ 
tion  in  aqua  regia,  by  adding  to  it  a  watery  dilution  of  green  vit¬ 
riol  (proto-sulphate  of  iron)  or  strips  of  metallic  copper.  Gold 
powder  may  likewise  be  obtained  from  the  same  solution  by  dis¬ 
tilling  it  to  dryness;  but  this  process  is  not  so  convenient  as  pre¬ 
cipitation.  The  powder  has  also  been  procured  by  first  forming 
in  amalgam  of  the  metal  with  mercury,  and  then  evaporating  the 
after ;  but  besides  being  expensive,  the  fumes  of  mercury  are 
bund  to  be  extremely  prejudicial  to  the  health  of  the  operators. 

When  gold  powder  is  used,  it  must  be  mixed  with  gum-water 
is  a  vehicle.  Where  it  is  intended  to  apply  leaf  gold  without 
my  fluxing  material  to  the  body  of  the  wares,  these  should  be 
noistened  in  the  requisite  parts  with  a  weak  solution  of  gum- 
rabic,  which  must  afterwards  be  allowed  to  dry.  When  the 
[■old  is  applied,  the  porcelain  or  glass  may  be  made  sufficiently 
dhesive  by  breathing  on  it.  If  a  flux  is  employed,  it  should, 
fter  being  rubbed  very  fine  with  a  muller,  be  diluted  with 
i'eak  gum-water,  and  very  thinly  spread  over  the  parts  which 

is  designed  to  ornament ;  when  very  nearly  dry,  the  leaf  gold 
1 5  laid  upon  it. 


82 


PORCELAIN  MANUFACTURE. 


CHAP.  VI. 


Japanners’  gold  size,  moistened  to  the  requisite  degree  with 
oil  of  turpentine,  is  sometimes  employed.  Waiting  then  until 
the  size  is  so  far  dried  as  to  be  only  clammy  to  the  touch,  the 
gold  leaf  is  laid  on  with  cotton  wool.  As  soon  as  the  gold  is 
applied,  the  ware  is  placed  in  an  oven  or  muffle,  that  it  may  be 
burnt  on. 

Some  old  authors  direct  the  artist  to  fuse  gold  with  regulus 
of  antimony,  to  pulverize  the  mass,  and  to  spread  the  powder 
upon  the  parts  to  be  gilded,  exposing  the  ware  afterwards  to 
such  a  heat  as  will  suffice  to  evaporate  the  antimony  while  the 
gold  remains  fixed.  This  method  of  proceeding  is  objectiona¬ 
ble,  from  the  almost  impossibility  of  spreading  the  powder  in  a 
sufficiently  uniform  manner,  besides  which,  part  of  the  gold  will 
also  be  carried  off,  and  some  descriptions  of  glass  are  even  fusi¬ 
ble  with  the  degree  of  heat  necessary  for  perfecting  the  process. 

Circular  gold  lines  are  frequently  described  on  small  articles, 
such  as  cups,  saucers,  and  plates.  To  assist  him  in  tracing 
these  with  accuracy,  the  artist  employs  a  portable  horizontal 
wheel,  the  height  of  which  may  be  adjusted  at  pleasure,  accord¬ 
ing  as  the  nature  of  the  work  requires  it  to  be  performed  in  a 
standing  or  a  sitting  posture.  The  lower  part  of  this  wheel  is 
somewhat  similar  to  the  leg  and  feet  of  a  claw  table,  the  leg 
being  bored  out  for  the  reception  of  a  stout  metallic  wire,  the 
altitude  of  which  is  regulated  by  means  of  a  thumb-screw. 

The  upper  or  movable  part  of  the  wheel  has  a  like  tubular 
cavity  in  its  vertical  part,  by  means  of  which  it  is  dropt  on  to 
the  upright  wire,  and  is  made  to  rest  upon  a  shoulder  fixed  on 
the  wire,  so  that  the  wheel  may  be  made  to  turn  truly  upon 
this  as  its  axis:  the  whole  is  surmounted  by  a  horizontal  table. 

In  proceeding  to  use  this  machine,  the  artist  places  his  feet 
firmly  upon  the  base  of  the  wheel,  and  fixing  the  article  to  be 
ornamented  upon  the  table,  he  causes  the  revolution  of  the 
wheel  with  his  left  hand,  and  holding  his  brush  steadily  in  the 
other,  describes  the  circles  with  the  utmost  facility  and  accu¬ 
racy. 

Burnishing,  which  is  the  last  process  performed  in  the  manu- ! 
facture  of  ornamented  porcelain,  is  usually  intrusted  to  female 
hands.  The  implements  required  for  this  purpose  are,  a  burn-; 
isher  of  agate  or  blood-stone,  some  white  lead,  a  piece  of  sheep¬ 
skin  for  wiping  the  ware,  and  some  vinegar.  As  extreme 
cleanliness  is  indispensable,  the  person  engaged  in  burnishing 
does  not  even  touch  either  the  porcelain  or  her  implements, 
but  interposes  between  them  and  her  hands  a  piece  of  clean 
white  linen.  The  agate  burnisher  should  be  applied  lightly! 
on  the  gilding,  following  all  the  ornaments,  and  never  rubbing 
in  cross  directions,  lest  the  gilding  should  appear  scratched. 


CHAP.  VI.  APPLYING  COLORS  AND  ENGRAVINGS.  83 

After  having  rubbed  the  gilding  for  some  time,  a  little  vinegar 
or  white  lead  should  be  applied  to  cleanse  the  surface.  Th^s 

b™nirTd  W,lth  a/°ft  linen  ra£’  the  burnishing  is  recom- 

the  thr°^hout  —  a 

be  r|membered,  that  in  the  preceding  description  of 

2  fcSr”  USm  ?  paintln"  porcelain,  several  were  mentioned 
as  being  unable  to  support  the  heat  of  the  gloss-oven.  Others 

Jl”’  have  not  this  disadvantage,  and  will  bear  the  highest 
emperature  without  injury.  Where  colors  are  applied  directly 

mixed  wiST1’  ?°  01i1S  ev,er."round  with  them,  but  they  are 
mixed  wuh  water  only,  and  the  glaze  may  be  added  without 

ename  kiln111^  appb«,tlonkof  heat  The  temperature  of  the 
enamel-kiln  is  usually  about  six  degrees  of  Wedgwood’s 

pyrometer,  answering  to  1857  degrees  of  Fahrenheit’s  “scale. 

In  the  year  1817,  the  Society  for  the  Encouragement  of  Arts 
&c.,  awarded  a  premium  to  Mr.  R.  Wynn,  for  a  list  of  receipts 

fluxSUnAatcd  ^  f°whe  PreParation  of  enamel  colors  and 

volume  of  the1?  °f  ^  1  paper  is  ™erted  ^  the  35th 
volume  of  the  Transactions  of  that  Society. 

The  fluxes  are,  No.  1.  Red  lead . 8  parts. 

Calcined  borax  .  .  II 

Flint  powder  ...  2' 

Flint  glass . 6 

No.  2.  Flint  glass  ....  10 

White  arsenic  ...  1 

Nitre . 1 

No.  3.  Red  lead . 1 

Flint  glass . 3 

No.  4.  Red  lead . 

Borax,  not  calcined  5j 

Flint  glass . 8 

No.  5.  Flint  glass . 6 

Flux,  No.  2 . 4 

Red  lead . 8 

The  ingredients  forming  each  of  these  fluxes  are  melted  to- 
,emer,  and  the  compounds  are  then  finely  pounded  for  use. 

1  he  recipes  for  colors  are  as  follows : — 

YeUow.  Red  lead  .  . . 8  parts. 

Oxide  of  antimony  ....  1 
White  oxide  of  tin  ....  1 
*nored>ents  well  in  a  biscuit-ware  mortar,  and  having 

hnia  P!?ce£f  Dutch  tile  in  the  make  grad- 

suffer  *  to  cool.  Take  of  this  mixture  1  part  ; 
ux’  iNo-  Grind  them  in  water  for  use.  By  varying 


84 


FORCELAIN  MANUFACTURE. 


CHAP.  VI. 


different  shades  of 


the  proportion  of  red-lead  and  antimony, 
color  may  be  obtained. 

Orange.  Red  lead . 12  parts. 

Red  sulphate  of  iron  ...  1 

Oxide  of  antimony  ....  4 

Flint  powder .  3 

after  calcining  these  without  melting,  fuse  one  part  of  the  com¬ 
pound  with  2|  parts  of  flux. 

Dark-red.  Sulphate  of  iron,  calcined  dark 


Flux,  No.  4.  .  6  parts 
Colcothar  .  .  1 
Light-red.  Red  sulphate  of  iron, 


of  this 


1  part. 
3 


1  part. 


Flux,  No.  1 . 3 

White  lead . 

Brown.  Manganese . 2^ 

Red  lead . 8| 

Flint  powder . 4 

The  style  of  decoration  described  in  the  preceding  pages  of 
this  chapter,  is  in  a  great  measure  confined  to  the  most  costly 
descriptions  of  porcelain.  Wares  which  are  fitted  by  their 
price  for  being  brought  into  more  general  use,  undergo  a  differ¬ 
ent  kind  of  embellishment.  A  great  variety  of  neatly  executed 
patterns  are  transferred  to  their  surfaces  from  impressions  pre¬ 
viously  printed  on  paper.  Before  the  introduction  of  this  style 
of  ornament,  table  services  of  home  manufacture  were  either 
composed  of  plain  Queen’s-ware,  with  occasionally  a  colored 
edge  ;  or  at  best  were  furnished  with  a  painted  border,  which 
displayed  but  little  taste  in  its  conception,  or  ability  in  its  exe¬ 
cution.  This  modern  improvement  has  added  materially  to  the 
decent  comforts  of  the  middle  classes  in  England,  and  has  more 
than  any  other  circumstance  contributed  to  the  great  extension 
of  our  trade  in  earthenware  with  the  continent  of  Europe. 
When  first  invented,  and  for  some  time  afterwards,  the  designs 
employed  were  only  imitations  of  figures  and  objects  seen  on 
old  blue  China  porcelain ;  but  a  better  taste  has  since  prevailed, 
and  artists  employed  in  the  composition  of  patterns  no  longer 
think  it  necessary  to  outrage  truth  in  their  representations. 
Landscapes  and  figures,  in  conformity  with  the  simplicity  of 
nature,  and  exhibiting  a  considerable  degree  of  taste,  are  now 
so  common,  that  this  new  advantage  derived  from  the  printing- 
press  is  enjoyed  without  exciting  attention  or  commanding  ac¬ 
knowledgment. 

The  method  of  transferring  printed  designs  to  earthem  ves¬ 
sels  is  thus  pursued.  The  landscape  or  pattern  is  engraved 
upon  copper,  and  the  color,  which  is  mixed  with  boiled  linseed 
oil,  is  laid  on  the  plate  in  the  same  manner  as  ink  is  usually; 


CHAr.  VI.  APPLYING  COLORS  AND  ENGRAVINGS.  85 

applied  by  copper-plate  printers.  To  increase  the  fluidity  of 
the  oil,  the  plate  is  then  temporarily  placed  in  a  stove,  a  sheet 
of  damped  tissue  paper  is  laid  on  it,  and  both  are  passed  in  the 
ordinary  manner  through  the  press.  The  paper,  wet  with  the 
color,  is  then  delivered  to  a  girl,  who  reduces  its  size  by  cut¬ 
ting  away  the  blank  portion  surrounding  the  pattern,  and  passes 
it  to  another  girl,  by  whom  the  impression  is  applied  lightly 
to  the  ware  when  in  the,  state  of  biscuit.  A  third  girl  is  next 
employed,  who,  with  a  piece  of  woollen  cloth  rolled  tightly  in 
the  form  of  a  cylinder,  rubs  the  paper  closely  against  the  piece, 
in  order  to  press  the  color  sufficiently  into  its  substance.  The 
paper  thus  rubbed  is  left  adhering  to  the  article  for  an  hour, 
when  both  are  placed  in  a-  cistern  of  water,  so  that  the  paper 
beepmes  soft  enough  to  be  peeled  off  without  violence,  having 
transferred  to  the  biscuit  the  impression  which  it  had  received 
from  the  copper-plate. 

When  the  pieces  thus  printed  have  stood  a  sufficiently  long 
time  to  become  dry,  they  are  placed  in  an  oven,  to  which  a 
gentle  heat  is  applied,  in  order,  by  dissipating  the  oil,  to  pre¬ 
pare  the  wares  for  receiving  the  glaze.  This  is,  of  course, 
completely  transparent,  as  otherwise  the  distinctness  of  the 
pattern  would  be  impaired. 

For  a  long  time  blue,  produced  from  the  oxide  of  cobalt,  was 
the  only  color  employed ;  but,  of  late,  the  potters  have  extend¬ 
ed  to  this  pleasing  branch  of  their  art  all  the  colors  on  their 
palette. 

The  glaze  on  printed  goods  is  vitrified  in  the  gloss-oven  in 
the  manner  already  described. 

The  French  potters  employ  a  different  method  for  transfer¬ 
ring  engraved  patterns.  They  cast  a  sheet  of  fine  glue,  about 
a  quarter  of  an  inch  thick,  and  diluted  while  warm  to  such  a 
degree  that  when  cool  it  shall  be  perfectly  flexible,  and  have 
the  consistence  of  leather.  This  glue  being  applied  upon  the 
plate,  and  pressed  with  the  hand,  receives  the  colors  according 
to  the  pattern,  which  it  gives  back  to  the  surface  of  any  vessel 
to  which  it  may  be  applied.  Two  impressions  may  generally 
be  given  in  this  manner  without  a  fresh  application  of  the  glue 
to  the  plate.  After  the  second  has  been  impressed,  the  surface 
of  the  glue  is  cleaned  carefully  with  water  applied  by  a  soft 
brush,  and  serves  again  as  before. 

The  decoration  of  earthenware  by  means  of  engravings  is  of 
much  more  recent  adoption  in  France  than  in  England, — not 
having  been  used  in  the  former  country  until  about  the  year 
1805. 

In  the  report  made  by  the  Committee  appointed  to  examine 
into  the  progress  of  the  arts  and  manufactures  in  France,  as 

II 


86 


TORCELAIN  MANUFACTURE. 


CHAP.  VII. 


exemplified  by  specimens  exhibited  at  the  Louvre  in  1819,  and 
to  which  report  allusion  has  already  been  made  in  this  Chapter, 
attention  is  drawn  to  a  curious  process,  whereby  a  porcelain 
manufacturer  was  enabled,  on  being  furnished  with  an  en¬ 
graved  copper-plate,  to  produce  impressions  on  any  scale  that 
might  be  required,  whether  larger  or  smaller  than  the  original. 
For  this  purpose  no  second  plate  of  copper  was  needed ;  and 
the  enlarged  or  diminished  copies  might  be  furnished  in  the 
course  of  a  very  few  hours.  It  is  to  be  regretted  that  no  de¬ 
scription  was  given  of  the  means  employed  for  effecting  this 
curious  process;  but  the  Committee,  who  personally  witness¬ 
ed  its  execution,  expressed  themselves  perfectly  satisfied  as  to 
its  efficiency,  and  awarded  an  honorary  gold  medal  to  the  in¬ 
ventor.* 


CHAP.  YH. 

ON  THE  MANUFACTURE  OF  TOBACCO  PIPES. 

This  Manufacture  prosecuted  to  a  great  extent. — Description  of  Material. — 
Rolling. — Boring. — Moulding.— Polishing. — Baking. — Description  of  Kiln 
— Of  Crucibles. — Manufacture  in  Holland. — Originally  conveyed  there 
from  England. 

The  manufacture  of  tobacco  pipes  forms  a  branch  of  the 
potter’s  art,  which  has  acquired  considerable  importance  from 
the  extent  to  which  it  is  prosecuted ;  and  it  is  at  the  same  time 
interesting  from  the  nature  of  the  processes  employed.  A  short 
account  of  these  will,  therefore,  not  be  thought  misplaced  in 
this  treatise. 

The  clay  chiefly  employed  for  the  purpose  is  found  in  the 
island  of  Purbeck,  in  Dorsetshire,  and  is  preferred  on  account 
of  its  extreme  whiteness.  Previously  to  being  used,  it  must 
be  diligently  purified  from  all  extraneous  matters.  The  means 
employed  for  this  latter  purpose,  being  the  same  as  have  al¬ 
ready  been  described,  their  recital  may  be  omitted  here. 

When  the  purification  is  accomplished,  and  the  clay  has  been 
formed  into  cubical  masses,  weighing  each  from  eighty  to  one 
hundred  pounds,  the  workman  from  time  to  time  cuts  off  small 
portions,  each  sufficient  to  form  one  pipe,  and,  first  kneading 
them  thoroughly  upon  a  table,  rolls  them  out  to  nearly  the 
form  and  size  of  pipes,  leaving  a  bulb  at  the  end  for  the  forma¬ 
tion  of  the  bowl.  In  this  operation,  the  skill  of  the  man  is 
made  apparent  by  the  near  approach  which  this  roll  makes  to 
the  dimensions  actually  required.  Persons  who  have  had  a 


*  Ann.  dc  Chim.  ct  dc  Phys.  tom.  \iii  p.  91. 


CHAP.  VII.  MANUFACTURE  OF  TOBACCO  PIPES.  87 

competent  experience  will  succeed  in  this  respect  to  such  a 
point  as  completely  to  fill  the  mould,  to  which  the  rolls  must 
afterwards  be  transferred,  leaving  but  little  surplus  clay  to  clip 
away. 

Fig.  5. 


When  the  rolls  have  been  formed  for  a  short  time,  and  by 
that  means  have  become  sufficiently  hardened,  the  workman 
proceeds  to  bore  the  stem  by  introducing  an  iron  needle.  This 
part  of  the  manufacture  calls  for  a  great  deal  of  address,  and 

'  Fig.  6. 


can  only  be  satisfactorily  accomplished  after  long  practice.  In 
performing  it,  the  roll  is  taken  between  two  fingers,  which  fol¬ 
low  the  point  of  the  needle  in  its  course  through  the  whole 
length  of  the  stem.  Near  to  its  point  the  needle  has  a  circular 
enlargement,  the  progress  of  which  may  be  felt  through  the 
substance  of  the  clay ;  and  thus  the  execution  of  the  task  is 
somewhat  facilitated.  The  bore  must  be  made  as  exactly  as 
possible  in  the  axis  of  the  stem ;  and,  in  forming  it,  the  needle 
must  be  pushed  forward  by  means  of  its  wooden  handle,  with 
a  gentle  and  equable  pressure.  The  part  which  is  to  form  the 
head  or  bowl  of  the  pipe  is  then  bent  so  as  to  give  it  the  proper 
inclination. 

The  mould,  into  which  the  stem  is  next  placed,  is  of  copper, 
and  divided  into  two  similar  parts.  On  being  put  to  use,  the 


Fig.  7. 


whole  interior  surface  of  both  sections  must  be  slightly  touched 
with  a  brush  containing  some  very  limpid  oil,  that  the  stem 
may  be  afterwards  delivered  from  it  without  difficulty.  The 
roll  of  clay  being  placed  in  one  section,  the  other  is  fitted  to  it 
according  to  marks  previously  made,  so  as  to  insure  the  perfect 
correspondence  of  the  two  parts.  The  mould  is  then  subject¬ 
ed  to  the  action  of  a  small  iron  press,  in  which  the  two  parta 


88 


PORCELAIN  MANUFACTURE. 


CHAP.  VII. 


are  forced  together  by  means  of  nuts  and  screws ;  and  by  this 
means  its  exterior  form,  with  all  its  ornamei  ts,  is  at  once  given 
to  the  pipe. 

The  head  or  bowl  has  yet  to  be  fashioned.  This  is  in  part 
effected  by  the  fore-finger,  and  more  perfectly  thereafter  by 
means  of  a  stamp  or  form  attached  to  the  mould,  and  which  by 
the  action  of  a  lever  is  introduced  within  the  hollow  which  the 
finger  has  made  for  the  purpose.  The  bore  of  the  stem  is  then 
continued  into  the  bowl,  by  pushing  the  needle  up  to  its  handle ; 
any  excessive  quantity  of  clay  that  may  have  been  used  is  next 
cut  away,  and  the  pipe  is  smoothed  by  means  of  an  iron  or  cop¬ 
per  blade. 

The  pipes  as  they  are  formed  are  spread  out  and  arranged 
upon  a  board,  that  they  may  be  still  further  dried ;  and  when 
they  have  acquired  a  certain  consistence,  any  roughnesses  that 
may  appear  upon  the  bowl  are  rubbed  away  with  an  appropri¬ 
ate  horn  instrument,  which  is  provided  with  a  groove,  of  which 
the  workman  avails  himself  to  perfect  the  circular  form  and  to 
smooth  the  edge  of  the  bowl. 

After  this  the  pipes  are  placed  a  second  time  in  the  moulds, 
that  any  imperfections  which  they  have  acquired  in  their  shape 
may  be  remedied ;  and  they  are  then  left  until  sufficiently  hard¬ 
ened  to  receive  the  last  polish,  which  is  given  by  rubbing  them 
with  flints  bored  with  holes,  some  of  which  are  of  the  same  di¬ 
ameter  as  the  stem,  wtfile  others  will  admit  the  head  of  the 
pipe.  If  it  should  then  appear  necessary,  the  workman  retouch¬ 
es  the  different  ornaments  on  the  pipe  with  a  kind  of  bodkin, 
and  the  needle  is  withdrawn  from  the  stem. 

These  various  operations,  which  bear  an  appearance  of  com¬ 
plexity  in  the  narration,  are  yet  so  easy  of  accomplishment, 
that  a  clever  moulder  will  furnish  3500  pipes  in  a  week. 

The  kiln  used  for  baking  the  pipes  is  cylindrical ;  having  a 
circular  fireplace  at  its  bottom.  With  the  exception  of  the 
spaces  required  for  the  circulation  of  heated  air,  the  interior 
of  the.  kiln  is  occupied  by  crucibles,  wherein  the  pipes  are 
placed.  These  crucibles,  which  are  made  very  thin,  are  com¬ 
posed  of  the  same  clay  as  the  pipes,  and  are  strengthened  by 
the  insertion  of  broken  pipe-stems.  The  bottoms  are  framed 
of  these  stems,  radiating  towards  the  centre,  and  having  the 
interstices  plastered  with  pipe  clay.  The  top  of  each  is  dome¬ 
shaped  ;  and  a  pillar  of  clay  is  placed  in  the  centre  through  the 
whole  altitude,  which  serves  at  once  to  strengthen  the  crucible, 
and  to  support  the  stems  of  the  pipes.  The  side  of  the  cruci¬ 
ble  is  provided  with  six  horizontal  ledges,  proceeding  at  equal 
distances  all  round,  and  upon  these  the  bowls  of  the  pipes  are 
arranged,  while  the  stems  are  made  to  lean  against  the  central 


CHAP.  VII.  MANUFACTURE  OF  TOBACCO  PIPES.  89 

pillar.  The  crucible  is  capable  of  containing  in  these  six  di¬ 
visions  fifty  gross  of  pipes ;  and,  if  the  heat  of  the  furnace  is 
properly  managed,  these  will  be  sufficiently  baked  in  seven  or 
eight  hours. 

Fig.  8 


The  property  possessed  by  tobacco  pipes  of  adhesiveness  to 
the  tongue,  is  owing  to  the  great  affinity  which  the  clay  has 
for  water:  this  quality  is  much  increased  by  the  baking  pro¬ 
cess. 

The  manufacture  of  tobacco  pipes  is  prosecuted  to  a  very 
considerable  extent  in  Holland,  whence  large  quantities  have 
long  been  exported  annually.  For  the  introduction  of  this  art 
the  Dutch  are  indebted  to  this  country ;  in  proof  of  which  as¬ 
sertion,  Mr.  Hollis,  who  passed  through  the  Netherlands  in 
1748,  mentions  that,  having  visited  very  extensive  pipe-works 
at  Gouda,  he  was  informed  by  the  master  of  it,  that  even  to 
that  day  their  principal  working  tools  bore  English  names. 


H2 


90 


PORCELAIN  MANUFACTURE. 


CHAP.  VIII. 


CHAP.  VIII. 

ON  THE  PORCELAIN  MANUFACTURE  OF  CHINA. 

Obscurity  wherein  its  Origin  is  shrouded — Chiefly  practised  at  King-te- 
Ching. — Supposed  Superiority  of  Old  China  Ware.— Materials  employed. 
— Kao-lin — Pe-tun-tse— Their  Preparation. — Oils  or  Varnishes— Their 
Composition. — Hao-che — Its  Superiority  to  Kao-lin.- — Analysis  of  Kao¬ 
lin. — Extent  of  Factories  at  King-te-Ching. — Great  Number  of  Workmen 
employed. — Preparation  of  Materials.— Method  of  fashioning  Utensils. — 
Moulds.— Division  of  Labor.— Deficiency  of  Chinese  in  the  Art  of  Design. 
— Their  Excellent  Colors. — Numerous  Hands  employed  in  Decorating  each 
Piece. — Bad  Effect  of  this  System. — Blue  long  the  only  Color  used  for 
Painting  China  Ware. — Mode  of  Preparing  various  Colors. — Chinese  ig¬ 
norant  of  Chemical  Science.— LTmiain. — Tsou-tchi. — Kia-tsing — Method 
of  forming  it. — Chinese  Furnaces. — Passion  for  Old  Porcelain. — Ku-tong. 
— Mock  Antiquities. — Reasons  for  Costliness  of  China  Ware  in  Europe. 
— High  Prices  formerly  paid  in  China. — Finest  Specimens  not  brought  to 
Europe. — Porcelain  Tower  at  Nan  king. — Chinese  Potters  prepare  Mate¬ 
rials  for  the  Use  of  their  Descendants. — Common  Wares  made  in  China. 
— Attempt  of  the  Emperor  to  transfer  the  Manufacture  to  Pekin.— His 
Want  of  Success. 

No  success  has  attended  any  efforts  that  have  been  made  to 
discover  the  origin  of  the  art  of  making  porcelain  in  China, 
and  the  date  of  its  invention  remains  veiled  in  obscurity.  The 
most  that  is  known  on  this  head  is  gathered  from  the  written 
annals  of  Feou-leang,  a  city  belonging  to  the  same  district  of 
the  empire  as  King-te-ching,  wherein  it  is  recorded  that,  from 
the  time  answering  to  the  year  442  of  the  Christian  era,  the 
last-mentioned  place  has  enjoyed  the  honor  of  supplying  the 
imperial  court  with  porcelain,  and  that  one  or  two  mandarins 
have  usually  been  deputed  from  Pekin  to  inspect  this  part  of 
the  workman’s  labors.  The  invention  of  the  art  would  assured¬ 
ly  date  from  a  much  earlier  period  than  that  here  mentioned ; 
as  it  would  be  long  ere  the  manufacture  arrived  at  such  a  state 
of  perfection  as  to  render  it  an  object  of  interest  to  the  court. 

It  is  a  very  common  opinion  in  China,  that  the  porcelain 
ware  made  by  their  ancestors  was  superior  in  quality  to  any 
more  recently  manufactured.  This  belief  is  grounded  on  the 
fact,  that  pieces  of  porcelain  are  frequently  dug  from  the  earth, 
which  are  uniformly  found  to  be  of  the  very  finest  description. 
It  has  been  remarked,  that  this  fact  is  not  by  any  means  con¬ 
clusive  evidence  upon  the  subject ;  the  buried  pieces  were 
most  probably  concealed,  during  periods  of  civil  commotion,  on 
account  of  their  value,  and  in  order  to  preserve  them  for  their 
owners,  who  were  without  an  equal  inducement  to  bury  arti¬ 
cles  of  more  common  use.  An  opinion  likewise  prevails,  and 
is  supported  by  reference  to  the  same  fact,  that  the  quality  of 
porcelain  vessels  is  improved  in  beauty  by  a  lengthened  burying 


CHAP.  VIII.  CHINESE  METHOD  OF  MANUFACTURE.  91 

in  the  earth  ;  and  the  same  answer  has  been  applied  to  this  as 
to  the  first-mentioned  assertion. 

The  Chinese  employ  in  the  composition  of  their  porcelain 
two  kinds  of  earths,  and  two  oils  or  varnishes.  Of  the  earths 
one,  which  is  called  kao-lin,  is  found  intermixed  with  particles 
of  a  shining1  substance  resembling  mica ;  the  other  is  known 
by  the^  name  of  pe-tun-tse,  and  is  of  a  brilliant  white,  exceed¬ 
ingly  fine  in  its  grain,  and  soft  to  the  touch.  Both  these  de¬ 
scriptions  of  earths  are  found  -in  mines  or  quarries  situated  be¬ 
tween  twenty  and  thirty  leagues  from  King-te-ching,  to  which 
place  they  are  brought  in  small  vessels,  which  are  continually 
passing  up  and  down  the  river  of  Jao-tcheou  for  that  purpose. 
The  hard  blocks  of  pe-tun-tse  are  cut  from  the  quarry  in  the 
form  and^  about  the  size  of  our  bricks,  and  are  brought  in  this 
state  to  King-te-ching.  The  first  preparation  which  these  lumps 
undergo,  is  that  of  breaking  and  pounding  them  coarsely  with 
iron  mallets,  and  afterwards  more  completely  in  mortars  with 
pestles,  wrought  either  by  the  hand  or  by  a  water-wheel.  By 
this  means  the  blocks  of  pe-tun-tse  are  reduced  to  an  almost 
impalpaple  powder,  which  is  thrown  into  an  urn-shaped  vessel 
nearly  filled  with  water,  and  then  stirred  briskly  about,  that  the 
particles  may  be  intimately  mixed  with  the  water.  When  this 
mixing  has  been  effected,  and  the  fluid  has  been  left  during  a 
short  time  to  repose,  a  white  creamy  substance  forms  upon  the 
surface,  to  the  depth  of  two  or  three  inches :  this,  being 
skimmed  off,  is  transferred  to  another  vessel,  supplied  with 
clear  water.  The  fluid  remaining  in  the  first  vessel  is  then 
again  stirred  up ;  another  portion  forms  upon  the  surface,  which 
in  its  turn  is  removed,  and  added  to  the  first  skimming;  and 
this  process  is  continued  as  long  as  any  creamy  substance  can 
be  collected  from  the  surface.  What  remains  in  the  urn-shaped 
vessel  has  not  been  sufficiently  ground  ;  and,  being  collected 
from  the  bottom,  must  be  again  submitted  to  the  process  of 
grinding. 

The  skimmings  are  left  to  settle  in  the  second  vessel,  until 
the  solid  portion  has  subsided  to  the  bottom,  leaving  the  super¬ 
natant  water  perfectly  clear:  this  is  then  poured  oft’;  the  sedi¬ 
ment  is  transferred  to  moulds,  wherein  it  remains  until  nearly 
dry ;  and  the  cakes  are  then  taken  out  and  cut  into  square 
pieces  of  the  size  most  convenient  for  use.  The  pe-tun-tse  is 
then  in  a  fit  state  for  combination  with  kao-lin ;  and  the  squares 
are  sold  by  the  hundred  to  the  porcelain  makers.  It  is  not  often 
that  the  manufacturer  can  venture  upon  using  this  material  in 
the  state  wherein  he  buys  it ;  the  men  who  have  been  previ¬ 
ously  employed  in  preparing  the  cakes,  most  generally  mix  in 
the  squares  as  large  a  portion  of  foreign  matter  as  they  expect 


92  TORCELAIN  MANUFACTURE.  CIIAP.  VIII. 

will  escape  detection :  a  separation  of  these  previously  to  the 
employment  of  the  eartli  becomes,  therefore,  needtuh 

A  similar  process  is  followed  in  the  preparation  ot  kao-lin ; 
but  this  substance  being  much  less  hard  than  pe-tun-tse,  less 
labor  is  required  for  its  performance. 

The  two  substances  described  as  oil  or  varnish  are  procured, 
one  from  a  combination  of  pe-tun-tse  with  another  mineral  sub¬ 
stance,  and  the  other  from  lime.  In  the  preparation  of  the  first 
of  these,  such  stones  are  preferably  selected  as  have  the  whitest 
appearance.  These  undergo  the  same  processes  of  grinding 
and  washing  as  have  already  been  described  ;  except  that  the 
creamy  substance,  when  it  has  subsided  in  tire  second  vessel, 
is  not  all  put  into  moulds,  but  only  the  upper  and  finer  stratum 
is  gathered  for  the  preparation  of  this  varnish.  To  each  one 
hundred  pounds  of  the  substance  thus  separated  one  pound  of  a 
mineral  called  she-kao,  which  is  a  kind  of  gypsum,  is  added. 
This  stone,  which  resembles  alum  in  its  appearance,  is  first 
raised  in  a  furnace  to  a  red  heat ;  and  then  reduced,  by  pound¬ 
ing  and  rubbing  in  a  mortar,  to  a  very  fine  powder  ;  in  which 
state  its  union  with  the  purified  pe-tun-tse  is  effected,  the  con¬ 
sistence  of  the  compound  being  perfectly  fluid. 

The  preparation  of  what  is  called  oil  of  lime ,  the  fourth  in¬ 
gredient  required,  is  thus  managed  : — Lumps  ot  quicklime  are 
first  sprinkled  with  water,  and  reduced  to  a  powder ;  upon  this 
a  bed  of  dried  fern  is  placed ;  then  another  layer  of  lime,  cov¬ 
ered  again  by  fern  ;  and  so  on  alternately,  until  the  pile  having 
reached  a  moderate  height,  fire  is  applied :  and  when  the  whole 
of  the  fern  is  consumed,  the  ashes  are  collected  and  strewn 
upon  fresh  beds  of  fern,  which  are  again  fired  ;  and  this  burn¬ 
ing  process  is  repeated  five,  six,  or  more  times  successively, — 
it  being  held  that  the  more  frequently  the  ashes  are  burnt,  the 
better  is  the  quality  of  the  product.  Some  ancient  Chinese 
annals  affirm  that,  instead  of  fern,  the  wood  of  a  kind  of  medlar 
tree  was  anciently  used ;  and  that  the  quality  of  the  porcelain 
was  in  consequence  more  beautiful.  This  wood  is  now  become 
too  scarce  to  be  employed  for  the  purpose.  The  lime  and  fern 
ashes  are  next  thrown  into  a  vessel  containing  fair  water,  and 
she-kao  is  added  in  the  same  proportion  as  to  the  creamy  dilu¬ 
tion  of  pe-tun-tse.  This  she-kao  dissolves ;  and  the  solid  matter 
being  separated  from  the  water  by  subsidence,  and  removed  in 
a  tolerably  fluid  state,  forms  what  the  Chinese  manufacturers 
call  the  oil  of  lime,  to  the  agency  of  which  they  attribute  all 
the  lustrous  appearance  of  their  porcelain.  Lime,  when  un¬ 
combined,  is  infusible,  except  at  a  very  intense  degree  of  heat ; 
and  the  fern  ashes  thus  added,  are  essential,  acting  as  a  flux, 
and  promoting  the  fusion  of  the  glaze  in  the  furnace.  In  mix- 


;hap.  viii. 


CHINESE  METHOD  OF  MANUFACTURE. 


93 


Inimfit  tI?  r:nishes  togetller’  on]y  one  measure  of  the  oil 
•r  lime  is  added  to  ten  measures  of  that  of  dp  tun  1  1 

ng  taken  that  the  consistence  of  both  is  Lai  ThP  i  f 
ime  is  easily,  and  to  tlie  seller  profitably,  adulterated  bv the 
ddHon  of  water,  combined  with  such  a 

It T,  ETT?  US  Pr°Puer  degree  of  consistency  °f  ^ 

iSSfr 

'hich  can  be  «dva„tageMuSr»Sd' intte  ^ 

ead  of  kao  lirTth68’  ^lf  CaPled  bao'cbe  1  and  when  used  in- 
ead  ot  kao-lin,  the  result  is  porcelain  of  very  fine  Pram  ex 

-edingly  light,  and  much  better  qualified  for  receiving-  colors* 

■t  more  brittle  and  far  dearer  in  its  cost,  than  the  Commoner 

r  kao  „r%h:e  price  °[  hao"cbe  being  three  times  that  paid 
kao-lin.  I  his  new  substance,  when  taken  from  the  mine 

idergoes  the  operation  of  a  careful  washing,  to  separate  from’ 

niK  i rtn  rVi"1  W,hlch  “  is  6u"d  aclr 

“  the,n  pounded,  and  treated  exactly  in  a  similar 

i?med  Th  ??  delCribed  m  the  Preparation  of  kao-lin.  It  is 
ed  that  hao-che,  thus  purified,  is  capable  of  beino-  made 

o  porcelain  without  any  admixture.  b 

,  Jf  tbe  kao-hn  which,  although  much  softer  than  the  ne- 

' "porcelain  a'nd  ^  ^  qUiarryI!  gives  strengtb  and  bodyPto 
IsfnTfi!  ’  d’  c°nse<luen,1y,  this,  or  some  substitute  pOS- 
°  same  quality,  forms  an  indispensable  ingredient  in 

rSr-5  11 13  \e}at?d  that  some  Europeans,  having  prh 

edytfemto  the0me  bl°Ck'S  of  Pe'tun-tse  in  Chma,  and^on- 
m  !  own  country,  vainly  endeavored  to  convert 

I nufacturer^thpv5  becoming  known  to  some  Chinese 

tacturers,  they  dendmgly  remarked,  “  that  certainlv  the 

ypwh"LTlbe  a  TmdeM  ^ S°  to S 

y  whose  flesh  was  to  sustain  itself  without  bones” 

s  ml,1"  kfnown’.from  the  particles  of  mica  which  it  con- 
,  °  have  its  origin  in  feispar,  or  graphic  granite.  It  is  in- 

ree  Tf^  ^  °[  a  porceIain  fumace  even  in  China,  the 
,1  f  YhlC  ,‘  mUf  be  most  tremendous,  as  some  of  the  ma- 

ne7»  P  °H?d  m  th?Ir  glazes  couId  not  be  vitrified  at  a  lower 
perature  than  would  suffice  to  fuse  Cornish  granite  The 

WeuTne68  °T  Chlna  agruB  Wkh  the  mines  0  Aiencon  and 
!  ar  Eimoges,  where  a  similar  earth  is  found— all 

eTextnT"/  SUpCr‘S“Um  of  red-  friable>  micaceous  rock, 
hund  tn  L  gneiss.  Tiie  constituent  ingredients  of  kao-lin 
und  to  be— silica  52,  alumina  42,  oxide  of  iron  0.33. 


94 


CHAP.  VIII 


PORCELAIN  MANUFACTURE. 

The  factories  employed  at  Kin^chmg 
as  dweUmgs  Ae  WOTtaa^  ^  ^  as  mUst  appea| 

S.'Ssssa  .■££ 35; srasji  s$sd 

>"Te  puriSS  ?  1° tStSta  has  been  complete 
by  the  processes  already  descnhed  th< inert option » toun' 

“Sea  •  “S  ver°  coatsest  descriptions,  the  kaodm  net! 

^e'SosUrrTon'r^t  5  toe  ThSe  operations  of  toe  fac 

ry,  is  that 

gather  so  as  to  form  , "^h TeSSd ZZ  cemented,  when 

lheP"  continuaUy^rample^upon  the  paste  bringing 

SSSS=H|S=^ 

lsS=SSi=|»3 

watef  or  Jobule  of  air  be  left  remaining  in  any  portion  of 
mass,r  the^ article  which  - 

spoiled  by  the  expansion  of  the  Win «•?»  woult[ 

SXS&SXMfc  ‘»e  poroela'e  *»  ™'  -  « 

“ffiec^rffSioned  by  the  Chinese  workmen  in  a  n 
ner  so  similar  to  that  adopted  in  our  own  potteries,  that 

1)6  The^  moulds  ^sed^n  The  potteries  of  China  for  forming  ph 
of  multSbrm  shape  are  made  in  several  ?or^s  or^, 
which  are  brought  together  when  used.  1  hey  are  ma 
yeltow  Unctuous  earth,  which  occurs  abundantly  mqnam«. 
L  Kino--te-chin<r ;  and  its  preparation  by  kneading  and 
is  veryshnilar  to  that  bestowed  on  the  porcelara  earths.  W 


3HAP.  VIII.  CHINESE  METHOD  OF  MANUFACTURE.  95 

i  uade  and  used  with  care,  these  moulds  will  last  for  a  long  time. 
The  Chinese  workmen  are  not  content  with  the  work  as  deliv¬ 
ered  from  the  moulds,  but  uniformly  finish  the  article  by  the 
•land,  using  a  variety  of  chisels  and  other  tools  to  touch  up  the 
various  lines  and  forms  given  by  the  mould,  as  well  as  to  sup¬ 
ply  its  probable  deficiencies;  so  that  the  potter  executes,  in 
some  sort,  the  art  of  a  sculptor.  •  In  works  where  different  ob¬ 
jects  appear  in  relievo,  these  are  made  separately,  and  added 
n  the  way  commonly  used  in  our  own  potteries. 

It  may  give  some  idea  of  the  number  of  hands  employed  in 
he  perfecting  of  every  piece  of  porcelain  to  state  what  D’En- 
recolles  has  related  to  occur  with  the  commonest  description 
if  tea-cup.  The  potter  has  the  management  of  the  wheel ;  and 
inder  his  hands  the  cup  assumes  its  form,  height,  and  diame¬ 
ter.  It  may  be  well  imagined  that  this  workman  does  not  be¬ 
stow  much  labor  upon  his  task,  when  we  are  told  that  for  fash¬ 
ioning  twenty-six  cups  he  receives  a  sum  equivalent  to  about 
jhree  farthings  of  our  money :  the  cup,  accordingly,  is  delivered 
y  him  in  a  very  imperfect  state  to  a  second  workman,  who  fits 
t  to  its  base.  From  him  it  passes  immediately  to  a  third  man, 
i'ho,  by  means  of  a  mould,  placed  on  a  kind  of  lathe,  corrects 
he  imperfections  of  its  shape.  A  fourth  man,  by  the  aid  of  a 
hisel,  corrects  the  inequalities  and  unevennesses  of  the  edges, 
nd  pares  the  cup  to  a  substance  which  renders  it  sufficiently 
•ansparent.  In  the  course  of  this  operation  he  has  frequently 
^course  to  water,  in  order  by  moistening  to  prevent  the  crack- 
lg  or  breaking  of  the  cup.  A  fifth  workman  then  smooths  the 
iside  by  turning  it  gently  on  a  mould.  Considerable  care  is 
?quired  in  this  stage  to  prevent  any  warping  or  the  formation 
f  any  cavity  in  the  cup.  Other  men  then,  according  to  the 
escription  of  cup  which  it  is  intended  to  produce,  add  either 
le  handle,  or  some  ornaments  in  relievo,  or  make  sunken  im- 
ressions.  The  operation  that  immediately  precedes  the  first 
iking  of  the  cup,  is  that  of  rounding  and  hollowing  the  inside 
'  its  foot :  this  is  performed  with  a  chisel. 

By  this  division  of  labor,  the  work  is  found  to  proceed  with 
'eater  regularity  and  rapidity.  Incessant  attention  to  one  op- 
•ation,  and  that  of  a  very  simple  kind,  gives  to  each  workman 
insiderable  dexterity  and  facility  in  its  performance ;  and  no 
ne  is  lost  in  the  changing  of  implements,  as  must  be  the  case 
one  man  had  to  conduct  the  manufacture  through  its  several 
liges. 

Very  large  pieces  of  porcelain  are  made  at  King-te-ching. 
hese  are  sometimes  of  such  magnitude,  that  they  must  first 
Jr  formed  in  two,  three,  or  more  sections;  each  one  of  which 
quires  to  be  supported  during  its  formation  by  three,  or  more 


96  PORCELAIN  MANUFACTURE.  CHAr.  VIII. 

men  When  the  different  portions  are  sufficiently  dry,  they 
are  united  together  with  slip,  in  the  same  manner  as  handles 
are  attached ;  and  the  seams  are  smoothed  and  polished  with  an 
iron  instrument,  so  that,  upon  their  being  afterwards  covered 
with  varnish,  it  is  not  possible  to  discern  the  points  of  junction. 

The  celebrated  traveller  Marco  Polo  mentions  the  vast  ex¬ 
tent  to  which  the  manufacture  was  carried  at  the  tune  ot  his 
residence  in  the  Celestial  Empire,  and  states  that  eight  porce¬ 
lain  cups  might  then  be  purchased  at  the  low  price  of  a  Vene¬ 
tian  groat*  ,  .  . 

Among  the  Chinese,  the  art  of  design  has  never  advancer 
beyond  the  very  first  steps.  These  people  appear  ignorant  of  the 
commonest  rules  of  perspective ;  and  their  drawing,  especially 
where  attempts  are  made  to  describe  the  human  figure,  it 
wretched  in  the  extreme.  To  make  some  amends  for  this,  the 
colors  which  they  employ  are  exceedingly  lively  and  brillian 
so  that  European  artists  have  found  it  a  difficult  task  to  vie  witl 
them  in  this  respect.  In  examining  the  painted  porcelain  ot 
this  singular  people,  one  is  almost  led  to  imagine  that  ther 
artists  have  been  debarred  the  sight  of  the  objects  which  the} 
attempt  to  represent,  as  otherwise  some  among  them  mus 
surely  have  possessed  sufficient  innate  taste  to  have  led  hin 
from  the  o-eneral  track,  and  instead  of  the  miserable  caricature 
that  disgrace  their  labors,  to  have  made  some  approach  toward 
the  truth  in  his  delineation  of  natural  objects. 

The  system  of  distributing  the  work  among  a  great  numbe 
of  hands,  which  is  found  so  successful  in  the  formation  of  porct 
lain,  is  also  pursued  in  the  painting  department.  One  artis 
forms  only  colored  circles  about  the  edges;  another  trace 
flowers,  which  a  third  paints ;  a  fourth  delineates  nothing  bu 
mountains ;  a  fifth  describes  water ;  a  sixth  traces  the  outline  o 
birds,  which  a  seventh  fills  up  with  colors.  Other  artists  trac 
and  color  animals ;  others  again  perform  the  same  tasks  wit 
the  human  figure,  and  in  this  way  every  object  of  art  and  nf 
ture  found  upon  their  porcelain  is  the  work  of  a  particula 
artist,  who  does  not  attempt  the  delineation  of  any  other  sul 
ject.  To  this  system,  so  useful  in  conducting  every  merely  m< 
chanical  operation,  may  possibly  be  owing  the  continued  ai 
herence  to  old  and  faulty  methods.  The  celerity  which  it 
calculated  to  produce  is  unfriendly  to  the  improvements  su{ 
gested  by  genius;  and  if  even  one  artist  among  the  crow 
should  be  found  with  taste  enough  to  aim  at  forming  and  en 
bodying  juster  conceptions,  his  approaches  to  nature  would  or 


*  Marsden’s  translation,  4to  edition,  page  560. 


CHAP.  VIII.  CHINESE  METHOD  OF  MANUFACTURE. 


97 


serve  to  render  more  glaring  the  deformities  produced  by  his 
fellow-laborers,  and  would,  therefore,  be  wholly  inadmissible. 

It  is  said,  that  for  many  ages  the  Chinese  used  only  white 
porcelain.  Tradition  adds,  that  its  whiteness  was  most  bril¬ 
liant,  that  the  pieces  were  altogether  faultless,  and  that  the 
only  name  by  which  they  were  known  when  exported  to  other 
kingdoms  was  that  of  “  the  precious  jewels  of  jao  tcheou.” 
Blue  was  the  first  color  wherewith  they  ornamented  pottery, 
but  the  employment  of  all  other  colors  very  speedily  followed 
upon  the  introduction  of  this  one.  At  first,  and  for  a  long 
time,  their  blue  color  was  prepared  from  a  very  fine  kind  of 
lapis  lazuli,  which  is  native  with  them  ;  but  they  now  import 
smalt  from  England,  at  a  price  so  much  below  that  which  their 
own  pigment  had  cost,  that  they  have  abandoned  its  manufac¬ 
ture,  and  depend  upon  their  foreign  supply.  The  fine  deep-blue 
sometimes  found  upon  specimens  of  old  Chinese  porcelain  is 
much  admired  and  valued  by  virtuosi ,  and  it  is  regretted  that 
this  color  is  not  used  at  present.  It  has  been  conjectured  that 
the  Chinese,  who  unquestionably  possess  cobalt,  most  probably 
employed  its  oxide  also  in  the  production  of  this  esteemed  blue 
color  before  they  were  enabled  by  their  commerce  with  Euro¬ 
peans  to  substitute  for  it  our  cheaper  pigment;  that  their 
method  of  preparing  the  ore  of  cobalt  was  such,  that  it  retained 
the  arsenic  with  which  it  is  always  found  in  combination,  and 
that,  consequently,  its  color  proved  much  deeper  and  richer 
than  the  preparation  made  by  us  from  the  same  mineral.  Our 
process  being  performed  in  a  reverberatory  furnace,  the  arsenic 
is  driven  off  in  fumes.  There  are  some  kinds  of  cobalt  which 
are  made  to  yield  smalt  without  this  previous  roasting,  and  the 
superior  color  which  in  such  case  is  always  produced  is  attribu¬ 
ted  to  the  presence  of  arsenic ;  since  if  this  mineral  be  added  to 
smalt  while  in  a  state  of  fusion,  the  color  will  be  rendered  much 
deeper.  The  preparation  of  smalt  from  cobalt  without  the  aid 
of  fire  is  more  expensive  and  the  produce  less  in  quantity  than 
where  the  common  process  is  followed.  The  French  manufac- 
j  turers  procure  their  smalt  by  dissolving  cobalt  in  nitric  acid 
(the  aqua  fortis  of  commerce),  and  then  precipitating ;  and  it 
might  be  well  for  our  porcelain  makers  to  try  the  effect  of  this 
method. 

The  red  color  used  by  the  Chinese  is  made  from  common 
!  green  vitriol  or  copperas  (proto-sulphate  of  iron),  which  goes 
with  them  by  the  name  of  tsa-fari.  This  material  they  calcine 
;  in  a  crucible,  continuing  to  apply  fire  for  so  long  a  time  as 
thick  black  fumes  are  seen  to  escape  from  a  hole  made  in  the 
top  of  the  crucible ;  but  when  these  fumes  are  succeeded  by  a 


98 


PORCELAIN  MANUFACTURE. 


CHAr.  VIII 


light  and  thin  cloud,  they  judge  that  the  process  has  been  car¬ 
ried  sufficiently  far,  and  remove  the  crucible  from  the  furnace, 
previously,  however,  withdrawing  a  small  quantity  of  the  color 
for  inspection,  as  the  test  here  mentioned  is  not  unerring. 
When  the  color  proves  good,  the  crucible  is  left  to  cool  gradu¬ 
ally,  a  cake  of  red  matter  is  then  found  at  the  bottom,  and  a  fur¬ 
ther  quantity,  in  the  form  of  fine  powder  adhering  to  its  sides. 
This  latter,  being  the  purest  and  finest  color,  is  kept  separate 
from  the  cake.  Copperas  affords  about  one  fourth  of  its  weight 
of  this  color,  which  alone  is  used  for  producing  all  the  various 
shades  of  red  in  the  porcelain  works  of  King-te-ching. 

White  porcelain,  made  in  China,  owes  much  of  the  fine  bril¬ 
liancy  of  its  color  to  the  oils  or  varnishes  before  described ;  but 
when  a  brighter  and  finer  hue  than  can  be  thus  produced  is 
needed,  a  mixture  of  the  following  kind  is  prepared.  The 
shores  of  some  of  their  rivers  furnish  a  species  of  agate,  which 
is  without  veins  and  nearly  transparent,  so  that  it  approaches 
to  the  nature  of  crystal.  This  stone  is  calcined  to  a  white  pow¬ 
der,  and  then  ground  as  fine  as  possible.  To  every  ounce  of 
this  they  add  two  ounces  of  white  lead  (ceruse,)  also  in  fine 
powder,  and  these  being  mixed  with  the  varnish,  the  whole  is 
laid  on  the  porcelain  in  the  same  way  as  other  colors.  Accord¬ 
ing  to  the  descriptions  given  to  us,  this  compound,  besides  be¬ 
ing  used  for  the  production  of  a  brilliant  white,  forms  also  the 
ground  or  basis  of  several  other  beautiful  colors.  Their  green, 
which  is  prepared  from  the  oxide  of  copper,  is  said  to  be  con¬ 
verted  into  a  fine  violet  color  by  admixture  with  the  white  just 
described.  Such  a  change  as  this  must  of  course  be  the  effect 
of  chemical  action  promoted  by  the  heat  of  the  furnace.  The 
mere  mechanical  mixture  of  white  with  green  would  only  re¬ 
duce  the  depth  of  its  shade.  A  very  small  proportion  of  the 
white  suffices,  it  is  said,  to  produce  a  very  deep  violet,  and  the 
hue  is  rendered  lighter  in  proportion  as  the  quantity  of  white  is 
increased.  Their  yellow  is  said  to  result  from  the  mixture,  in 
due  proportions,  of  this  white  with  copperas  (proto-sulphate  of 
iron).  The  accounts  we  have  of  those  processes  among  the 
Chinese,  which  depend  upon  chemical  laws,  are  given  with  so 
little  regard  to  accuracy,  and  betray  so  great  a  want  of  scien¬ 
tific  acquirement,  that  these  descriptions  of  their  mode  of  pre¬ 
paring  colors  cannot  be  received  with  any  satisfaction. 

The  Chinese  painters  of  porcelain  usually  mix  their  colors 
with  gum  water,  in  which  a  small  portion  of  either  saltpetre 
(nitrate  of  potass),  white  lead,  or  copperas  has  been  first  dis¬ 
solved.  Where  a  red  color  is  used,  the  porcelain  oil  or  varnish 
is  applied  with  it.  This  color  is  laid  on  the  ware  when  in  the 
state  of  biscuit,  that  is,  when  it  has  been  once  in  the  oven,  but 


CHAP.  VIII.  CHINESE  METHOD  OF  MANUFACTURE.  99 

it  requires  the  heat  of  the  second  baking  to  bring  out  all  its  re¬ 
quisite  shades  and  tints. 

Black  porcelain,  ornamented  with  gold,  known  under  the 
name  of  umiam,  is  much  esteemed  in  the  East.  The  black  is 
produced  by  mixing  three  drachms  of  deep  blue,  with  seven 
drachms  of  the  varnish,  which  they  call  oil  of  stones.  The  black 
thus  prepared  is  laid  on  when  the  porcelain  is  first  dried,  and 
when  the  black  is  also  thoroughly  dry,  the  vessel  is  baked. 
The  gold  is  then  laid  on,  and  the  piece  is  subjected  to  another 
baking  in  a  furnace  peculiarly  constructed  for  the  purpose. 
The  gold  is  ground  in  water  to  a  very  fine  powder ;  and  when 
this  has  been  very  gradually  dried  in  the  shade,  one  tenth  of  its 
weight  of  white  lead  is  added,  the  mixture  is  incorporated 
with  gum  water,  and  laid  on  in  the  same  manner  as  colors  are 
applied. 

The  Chinese  have  a  kind  of  porcelain,  which  is  in  much  re¬ 
pute  with  them,  called  tsou-tchi.  This  has  the  appearance  of 
having  been  broken,  and  of  having  its  fractured  edges  brought 
together  and  cemented,  and  then  covered  with  the  varnish  ori¬ 
ginally  used.  This  effect  is  produced  through  the  peculiar  na¬ 
ture  of  the  varnish  employed,  which  never  spreads  evenly,  but 
has  a  tendency  when  in  fusion  to  run  into  veins  and  ridges  of 
various  and  uncertain  forms.  This  varnish  is  made  from  a  sort 
of  agate  stones,  reduced  by  calcination  to  a  white  powder, 
which  after  being  long  ground  in  a  mortar  is  carefully  washed, 
and  used  when  of  the  consistence  of  cream.  It  has  been  sug¬ 
gested  that  crystal  would  probably  answer  this  purpose  as  well 
as  the  coarse  agates  of  the  Chinese ;  and  among  all  the  de¬ 
mands  of  fashion  which  is  ever  seeking  for  something  new,  it 
might  perhaps  serve  the  interest  of  some  manufacturer  to  put 
this  suggestion  to  the  proof. 

Another  kind  of  porcelain,  much  esteemed  by  the  Chinese, 
is  called  by  them  kia-tsing ,  which  signifies  pressed  azure.  In 
vessels  of  this  description  the  colors  appear  only  when  the 
cups  are  filled  with  liquid.  The  manner  of  making  porcelain 
so  as  to  produce  this  effect  is  as  follows : — The  cup  is  made 
very  thin,  and  after  having  been  once  baked,  the  colors  are  ap¬ 
plied  in  the  required  forms  on  its  inner  surface.  When  dry,  a 
coating  of  porcelain  earth,  the  same  as  that  already  composing 
the  cup,  must  be  laid  on  the  inside ;  over  this,  the  usual  varnish 
is  laid,  so  that  the  colored  figures  are  inclosed  between  two 
coats  or  bodies  of  the  ware.  The  outside,  already  very  thin,  is 
then  ground  down  almost  to  the  painted  figures,  which  are 
thus  made  to  appear  externally,  when  they  must  be  covered 
anew  with  a  coat  of  varnish  so  as  to  be  scarcely  perceptible 
from  the  outside,  until  the  vessel  being  filled  with  liquid,  this 


100 


PORCELAIN  MANUFACTURE. 


CHAP.  VIII. 


acts  as  a  kind  of  foil  behind,  and  throws  ont  the  figures  which 
before  were  obscured.  So  much  carefulness  is  called  for  in 
the  production  of  kia-tsing,  that  the  art  is  very  seldom  prac¬ 
tised. 

Another  admired  art  among  this  people  is  that  of  producing 
the  semblance  of  various  figures  upon  pure  white  porcelain, 
whose  surfaces  are  yet  entirely  smooth.  Having  fashioned  a 
vessel,  with  the  finest  materials  and  extremely  thin,  it  must  be 
polished  inside  and  out,  when  a  stamp  cut  with  the  requisite 
figures  in  relief  must  be  pressed  upon  the  inner  surface  of  the 
unbaked  vessel.  The  finest  white  varnish  must  next  be  applied 
over  its  entire  surfaces,  so  that  the  cavities  impressed  by  the 
stamp  are  filled  by  it,  and  the  smoothness  of  the  inner  surface 
is  restored.  When  the  ware  is  baked,  the  varying  thicknesses 
of  the  more  opaque  varnish  will  be  apparent  through  the  trans¬ 
parent  sides  of  the  cup,  and  the  wThole  of  the  figures  will  then 
be  seen  as  finely  and  accurately  traced  as  if  painted  on  the  out¬ 
side. 

The  methods  employed  by  the  manufacturers  of  King-te- 
ching  in  applying  the  varnish,  vary  with  the  different  qualities 
of  the  wares  under  operation.  For  very  fine  and  thin  porce¬ 
lain  two  exceedingly  thin  coatings  are  very  carefully  applied, 
and  some  dexterity  is  required,  both  with  regard  to  the  quantity 
laid  on,  and  the  equable  manner  of  its  application.  To  pieces 
of  inferior  quality,  as  much  varnish  is  applied  in  one  coating 
as  is  comprised  in  the  two  layers  just  mentioned.  The  foot  of 
the  vessel  is  never  properly  formed  until  this  stage  of  the 
manufacture,  and  after  the  painting  and  varnishing  have  been 
completed,  when  this  part  is  finished  on  the  wheel,  and  var¬ 
nished  likewise.  The  work  is  then  fit  to  be  placed  in  the  oven. 

The  construction  of  furnaces  and  the  system  followed  in 
baking  porcelain  in  China  differ  so  little  from  the  structure  and 
method  pursued  in  England,  that  little  need  be  said  here  con¬ 
cerning  them.  It  has  already  been  mentioned  that  the  nature 
of  the  materials  employed  calls  for  a  much  higher  degree  of 
heat  than  is  necessary  in  our  potteries.  To  insure  this,  the 
Chinese  are  very  careful  in  providing  a  rapid  draught,  and  in 
the  incessant  feeding  of  their  furnaces  with  small  billets  of 
wood,  so  as  to  insure  its  most  rapid  combustion.  The  learned 
Jesuit  D’Entrecolles  observes,  as  a  thing  quite  unaccountable, 
and  even  inconceivable,  if  he  had  not  witnessed  the  fact,  that 
notwithstanding  the  enormous  consumption  of  wood  during  so 
many  hours,  none  of  its  ashes  are  ever  found  upon  the  hearth 
of  the  oven.  There  would  have  been  greater  reason  for  aston¬ 
ishment  had  the  contrary  fact  appeared.  The  rapid  draught 
excited  by  the  disposition  of  the  oven,  and  the  excessive  degree 


CHAP.  VIII-  CHINESE  METHOD  OF  MANUFACTURE.  101 

of  its  temperature,  would  serve  to  carry  away  completely 
through  the  flue  so  light  a  substance  as  wood  ashes. 

The  taste  for  old  porcelain  appears  to  prevail  fully  as  much 
in  China  as  it  has  ever  done  in  this  country.  It  is  asserted  by 
some  persons,  that  such  as  was  made  in  former  days  was  not 
only  composed  of  finer  materials,  but  was  more  perfect  in  the 
mode  of  its  manufacture.  Unfortunately  for  this  assertion, 
there  are  workmen  at  King-te-ching,  who  make  it  their  occu¬ 
pation  to  counterfeit  these  much-coveted  relics  of  antiquity, 
which  are  called  ku-tong,  and  in  this  they  succeed  so  as  to  de¬ 
ceive  the  most  observant  connoisseurs.  In  the  preparation  of 
these  mock  antiques  there  is  but  little  variation  from  the  meth¬ 
ods  usually  practised.  They  are  made  thicker  than  modern 
porcelain,  and  are  made  to  undergo  the  ceremony  of  burial  for 
one  or  two  months  in  the  most  lothesome  sink  of  filth  which 
can  be  found,  by  which  means  every  appearance  of  newness  is 
effaced. 

Several  reasons  are  assigned  for  the  high  price  at  which 
Chinese  porcelain  is  sold  in  Europe.  One  of  these  is,  that  owing 
to  their  very  unscientific  manner  of  conducting  the  baking 
process,  it  rarely  happens  that  some,  and  sometimes  a  very  con¬ 
siderable  portion,  is  not  spoilt  by  unequal  or  excessive  heat,  and 
converted  to  a  deformed  and  shapeless  mass.  Another  reason 
for  dearness  is,  the  constantly  diminishing  supply  of  the  mate¬ 
rials  used,  and  more  especially  of  fuel,  which  becomes  very  ex¬ 
pensive.  It  is  added,  that  as  those  pieces  which  are  prepared 
for  the  markets  of  Europe,  are  of  patterns  unacceptable  to  the 
taste  of  home  consumers,  and  as  the  factors  are  exceedingly 
particular  in  rejecting  every  article  which  exhibits  the  slightest 
defect  either  in  form  or  color,  the  prices  paid  to  the  manufac¬ 
turers  for  such  as  are  accepted  must  be  sufficiently  high  to  in¬ 
clude  the  cost  of  those  which  are  rejected.  Notwithstanding 
these  circumstances,  the  prices  at  which  porcelain  is  now  fur¬ 
nished  in  China  are  materially  less  than  those  demanded  in  an¬ 
cient  times,  when,  we  are  informed,  as  much  as  100  crowns 
were  given  for  a  single  urn  at  the  seat  of  manufacture.  The 
emperor  monopolizes  the  finest  specimens  of  porcelain  manu¬ 
factured  in  his  dominions,  and  it  lias  thence  been  asserted,  that 
none  which  has  ever  found  its  way  to  Europe  gives  an  adequate 
idea  of  the  perfection  to  which  the  Chinese  have  attained  in 
this  manufacture.  The  Porcelain  Tower  erected  at  Nan-king 
offers  proof  sufficient  of  the  very  durable  nature  of  their  manu¬ 
facture.  This  building  is  of  an  octagonal  shape,  is  of  nine  sto¬ 
ries,  and  very  nearly  300  feet  high,  and  its  entire  surface  is  co¬ 
vered  with  porcelain  of  the  finest  quality.  Although  this  sin¬ 
gular  and  beautiful  edifice  has  been  erected  more  than  400 

12 


102  FOUCELAIN  MANUFACTURE.  CHAP.  VIII. 

years,  it  has  hitherto  withstood  all  the  alternations  of  seasons, 
and  every  variety  of  weather,  without  exhibiting  the  smallest 
symptom  of  deterioration. 

The  intimate  mixture  of  the  two  earthy  materials  so  essen¬ 
tial  to  the  production  of  good  porcelain  is  much  more  perfectly 
attained,  if,  after  the  employment  of  the  mechanical  means  al¬ 
ready  described,  the  united  mass  be  left  for  a  considerable  time 
before  its  employment.  The  Chinese  frequently  extend  this 
interval  to  a  space  of  fifteen  or  twenty  years ;  and  instances  are 
not  uncommon,  where  the  provident  care  of  a  parent  leads  him 
to  prepare  as  much  porcelain  clay  as  will  suffice  for  his  son’s 
use,  during  the  whole  period  of  his  life. 

The  Chinese  excel  in  the  manufacture  of  brown  earthen¬ 
ware,  which  being  sold  at  a  very  low  price,  is  used  commonly 
throughout  the  empire.  Porous  vessels  for  cooling  water  are 
also  made  by  them  of  fuller’s  earth,  which  is  principally  com¬ 
posed  of  alumine  and  very  pure  silex,  in  combination  with  oxide 
of  iron.  The  name  by  which  porcelain  is  distinguished  in  this, 
the  country  of  its  earliest  production,  is  tse-ki. 

An  attempt  was  once  made  by  the  government  to  remove  the 
seat  of  manufacture  to  the  imperial  city  of  Pekin.  This,  how¬ 
ever,  although  no  effort  was  spared  in  the  business,  proved  un¬ 
successful,  and  the  sole  prosecution  of  the  art  reverted  to  King- 
te-ching,  where,  according  to  the  statement  of  different  travel¬ 
lers,  there  are  established  500  factories,  giving  employment  to 
more  than  a  million  of  artisans.  There  appears  no  good  reason 
for  believing  that  the  manufacture  would  not  have  been  prose¬ 
cuted  with  equal  success  at  Pekin,  if  those  who  directed  it  had 
been  so  disposed;  and  the  different  result  which  has  been  re¬ 
corded  is  supposed  to  have  arisen  from  the  disinclination  of  the 
manufacturers  to  be  brought  so  closely  within  the  control  of  a 
government  supereminently  famed  for  meddling  with  the  pri¬ 
vate  concerns  of  its  subjects. 


MANUFACTURE 

or 


GLASS. 


A 


TREATISE 

ON  THE 

PROGRESSIVE  IMPROVEMENT  AND  PRESENT  STATE 

OF  THE 

MANUFACTURE  OF  GLASS. 


CHAPTER  I. 

ON  THE  NATURE  AND  PROPERTIES  OF  GLASS,  AND  THE  HIS¬ 
TORY  OF  ITS  MANUFACTURE. 

Nature  of  Glass.— Its  various  Properties.— Its  Utility.— The  Assistance  it 
lends  to  Science.— Excessive  Prices  formerly  paid.— Origin  of  its  English 
Name.— Aristotle’s  Problems.— First  Invention  ascribed  to  the  Phmni- 
cians.— Manufactories  of  Alexandria.— Utensils  found  in  Herculaneum. 
— Malleable  Glass. — Tax  on  Glass  by  Alexander  Severus. — Portland  Vase 
—Glass  employed  in  forming  Windows.— Privileges  granted  to  Manufac¬ 
turers  in  France. — Plate-Glass  Casting. — Establishment  at  St.Gobain. _ Its 

early  Failure,  and  Revival. — Manufacture  commenced  in  England.— Of 
Flint  Glass.— Of  Plate  Glass.— Chinese  unacquainted  with  Glass-making 
—Importance  of  the  Manufacture  in  England.— Glass  made  a  Source  of 
Revenue. 

Many  circumstances  contribute  to  render  glass  one  of  the 
aost  curious  and  interesting  of  manufactured  substances. 

.  Although  perfectly  transparent  itself,  not  one  of  the  mate¬ 
rs  of  which  it  is  made  partakes  of  that  quality.  Exceedingly 
rittle  while  cold,  it  becomes,  by  the  application  of  heat,  so  re¬ 
markably  flexible  and  tenacious  as  to  be  convertible  into  every 
)rm  that  fancy  may  dictate  or  convenience  suggest.  Its  great 
uctility  is  shown  in  a  very  striking  mannerly  the  slender 
laments — small  as  the  fibres  of  spider’s  web — into  which  it  is 
)un  for  ornamental  purposes.  Many  hundred  feet  of  these 
laments  may  be  drawn  out  from  a  heated  mass  in  the  space 
'one  minute.  Its  pliancy  and  elasticity  are  proved  by  the 
j  cility  with  which,  when  in  the  state  just  mentioned,  it  may 
m  bent  and  retained  in  various  forms,  and  by  the  energy 
herewith  its  original  shape  is  resumed  at  the  moment  of  re- 
ase  from  its  constrained  position. 

!  The  impermeability  of  glass  to  water,  even  under  a  consid- 
able  degree  of  pressure,  is  well  ascertained.  A  few  years 
1°,  the  reverend  Mr.  Campbell,  while  on  a  voyage  to  South- 
n  Africa,  among  other  philosophical  experiments  wherewith 
•  amused  himself,  caused  two  globular  glass  bottles  hermet- 
illy  sealed  to  be  lowered  by  means  of  leaden  weights  to  the 
pth  of  1200  feet  beneath  the  surface  of  the  sea.  These, 


106  MANUFACTURE  OF  GLASS.  CHAP.  I. 

through  the  united  and  continuous  exertions  of  ten  men  during 
fifteen  minutes,  were  again  drawn  up,  and  were  found  to  be 
perfectly  empty. 

The  continued  exposure  of  glass  to  the  greatest  heat  where¬ 
by  it  is  melted,  does  not  produce  any  sensible  diminution  in  its 
weight  and  quantity,  or  any  alteration  of  its  properties.  It  is 
capable  of  receiving  colors,  and  of  retaining  them  in  all  their 
lustre  for  an  indefinite  period.  The  strongest  acids— with  one 
exception  that  will  be  noticed — have  no  efiect  upon  it,  a  cir¬ 
cumstance  that  renders  glass  additionally  useful  in  assisting 
the  researches  of  chemists.  It  is  capable  of  receiving  the 
most  perfect  polish,  preserves  all  its  beauty,  and  does  not  lose 
the  smallest  portion  of  its  substance  by  the  longest  and  most 
frequent  use. 

The  admirable  qualities  and  important  uses  of  glass  have 
been  so  happily  pointed  out  by  one  of  the  most  celebrated 
writers  of  the  last  century,  that  no  apology  will  be  needed  for 
the  insertion  of  the  passage. 

“  Who,  when  he  saw  the  first  sand  or  ashes  by  a  casual  in¬ 
tenseness  of  heat  melted  into  a  metalline  form,  rugged  with 
excrescences,  and  clouded  with  impurities,  would  have  im¬ 
agined  that  in  this  shapeless  lump  lay  concealed  so  many  con¬ 
veniences  of  life  as  would  in  time  constitute  a  great  part  of  the 
happiness  of  the  world  1  Yet  by  some  such  fortuitous  liquefac¬ 
tion  was  mankind  taught  to  procure  a  body  at  once  in  a  high 
degree  solid  and  transparent,  which  might  admit  the  light  of 
the  sun,  and  exclude  the  violence  of  the  wind ;  which  might 
extend  the  sight  of  the  philosopher  to  new  ranges  of  existence 
and  charm  him  at  one  time  with  the  unbounded  extent  of  thf 
material  creation,  and  at  another  with  the  endless  subordina¬ 
tion  of  animal  life  ;  and  what  is  yet  of  more  importance,  migh 
supply  the  decays  of  nature,  and  succor  old  age  with  subsidiar) 
sight.  Thus  was  the  first  artificer  in  glass  employed,  though 
without  his  own  knowledge  or  expectation.  He  was  facilitat 
ing  and  prolonging  the  enjoyment  of  light,  enlarging  the  ave¬ 
nges  of  science,  and  conferring  the  highest  and  most  lasting 
pleasures;  he  was  enabling  the  student  to  contemplate  nature 
and  the  beauty  to  behold  herself.”  * 

The  utility  of  a  substance  which  is  daily  and  hourly  renders 
serviceable  by  all  classes  of  persons  in  almost  every  humai 
habitation  cannot  need  to  be  exemplified.  The  aids  which  i 
offers  to  scientific  researches  are  almost  equally  apparent.  Ti 
notice  the  particular  arrangements  whereby  the  chemist,  thf 
naturalist,  or  the  astronomer  avails  himself  of  some  of  the  va 


*  Rambler,  No.  U. 


CHAP.  I. 


HISTORICAL  NOTICES. 


107 


nous  properties  of  glass  in  pursuing  his  investigations,  would 
lead  to  descriptions  which*  although  interesting  in  a  hioh  de- 
gree,  are  foreign  to  the  object  of  this  treatise,  wherein  little 
more  than  incidental  notices  can  be  given,  on  points  that  have 
relation  to  improvements  in  the  manufacture. 

It  may  be  useful,  however,  to  notice  here  an  error,  not  un- 
frequently  made,  from  observing  glass  to  be  the  only  transpa¬ 
rent  material  used  in  making  spectacles,  opera  glasses,  and 
other  optical  instruments.  Persons  are  induced,  from  this  cir¬ 
cumstance,  to  ascribe  to  the  peculiar  quality  of  glass  the  ex¬ 
clusive  power  of  modifying  the  apparent  magnitude,  brightness, 
and  distinctness,  of  objects  seen  through  it.  This,  however  is 
not  an  exclusive  property  of  glass,  but  belongs  to  every  trans¬ 
parent  substance  having  a  density  different  from  that  of  the  air 
which  surrounds  the  observer.  It  depends  also,  not  alone  on 
the  inherent  qualities  and  density  of  the  transparent  substance 
through  which  the  objects  are  viewed,  but  also  on  the  form  of 
the  surfaces  which  bound  that  substance,  and  on  various  other 
circumstances  not  necessary  to  be  noticed  more  particularly 
here.  The  reader  will,  therefore,  recollect,  that  the  optical 
properties  of  glass  are  common  to  the  diamond  and  other  trans¬ 
parent  solids,  to  all  transparent  liquids,  and  even  to  gases 
Wass  is  commonly  used  on  account  of  its  cheapness  and  dura- 
bility,  and  for  other  reasons  of  convenience. 

It  is  impossible,  however,  wholly  to  dismiss  this  subject  un¬ 
accompanied  by  expressions  of  admiration  at  the  genius  of  those 
master  spirits,  who,  by  their  discoveries  and  inventions,  have 
rendered  glass  subservient  to  purposes  that  open  and  enlarge 
the  held  of  human  knowledge  in  some  of  those  branches  of  nat¬ 
ural  philosophy  which  tend  most  to  refine  the  nature  and  exalt 
the  character  of  man. 

Familiarized  as  we  are  to  the  use  and  appearance  of  glass, 
fet  no  person  can  ever  become  indifferent  to  its  advantages,  or 
nsensible  to  its  beauty.  Neither  can  we  feel  astonishment  at 
he  admiration  which  induced  the  ancients,  while  the  art  of 
na  ing  it  was  little  practised,  and  in  those  countries  where  it 
■vas  not  yet  established,  so  greatly  to  covet  the  possession  of 
pass  vessels  as  to  purchase  them  at  prices  which  to  us  appear 
‘xorbitant.  We  are  told  that  the  emperor  Nero  gave  for  two 
handles  6000  sestertia,  a  sum  nearly  equal  to 
»U,UUUZ.  of  our  money.  These  vessels  were  not  of  any  extra- 
'rdinary  size,  but  were  thus  highly  valued  on  account  of  their 
'ertect  transparence,  and  resemblance  to  crystal. 

The  name  whereby  this  material  is  known  to  us  is  generally 
ai .  0  derived  from  the  Latin,  and  to  have  been  suggested 
y  its  great  similarity  in  appearance  to  ice  ( glacies .)  It  has 


108 


MANUFACTURE  OF  GLASS. 


CHAP.  I. 


been  remarked,  however,  that  the  common  Latin  designation 
is  vitrum ;  and  as  the  Romans  gave  this  name  also  to  the  plant 
which  we  call  woad,  and  which  our  remote  ancestors  called 
glastum,  it  is  imagined  that  glass  obtained  the  same  distinctive 
appellation,  because  of  the  bluish  tint  which  it  usually  exhib¬ 
ited.  There  is  as  little  probable  foundation  for  one  as  for  the 
other  conjecture,  nor  is  the  question  of  much  importance,  since, 
whichever  way  it  might  be  determined,  no  light  would  be 
thereby  thrown  upon  any  point  of  interest  concerning  the  origin 
of  the  manufacture,  which,  although  involved  in  the  most  im¬ 
penetrable  mystery,  is  yet  known  to  have  existed  long  before 
its  introduction  among  the  Romans. 

The  passage  in  the  book  of  Job  (ch.  xxxvii.  v.  18.)  wherein 
mention  is  supposed  to  be  made  of  glass,  has  been  adduced  by 
Neri  in  proof  of  its  remote  origin.  Unfortunately  for  the  cor¬ 
rectness  of  this  opinion  it  has  been  found,  that  in  many  ancient 
versions,  instead  of  the  glass  of  the  Vulgate  and  Septuagint, 
other  substances  which  have  diaphanous  and  shining  properties 
are  mentioned.  In  fact,  the  word  in  the  original  Hebrew  lias 
been  frequently  used,  according  to  the  fancy  of  translators,  to 
signify  different  bodies  possessing  lustre  and  transparency. 

The  two  problems  of  Aristotle — if,  indeed,  they  were  pro¬ 
pounded  by  that  philosopher — “Why  do  we  see  through 
glass  1”  and  “Why  is  it  not  malleable  1”  comprise,  perhaps, 
the  earliest  written  mention  made  of  the  substance.  Theo¬ 
phrastus,  whose  writings  are  not  half  a  century  later  than  the 
time  of  Aristotle,  mentions  the  use  of  sand  from  the  river  Belus 
in  making  glass ;  and  from  that  date  (300  years  b.  c.)  a  know¬ 
ledge  of  the  material  was  pretty  generally  diffused.  If  reli¬ 
ance  is  to  be  placed  upon  the  statement,  that  the  celebrated 
sphere  of  Archimedes  was  made  of  glass,  the  art  must  in  his 
time  (209  years  b.  c.)  have  arrived  at  a  considerable  degree  of 
perfection. 

Many  authorities  concur  in  assigning  the  merit  of  the  inven¬ 
tion  to  the  Phoenicians ;  and  the  assertion  of  Pliny  is  often  re¬ 
peated,  which  attributes  the  discovery  to  accident.  Some 
storm-driven  mariners  were  boiling  their  food  on  the  sands  at 
the  mouth  of  the  river  Belus — a  small  stream  running  from  the 
foot  of  Mount  Carmel  in  Galilee — where  the  herb  kali  was 
growing  abundantly,  and  are  said  to  have  perceived  that  the 
sand,  when  incorporated  with  the  ashes  of  this  plant,  melted 
and  ran  into  a  vitreous  substance.  It  is  certain  that  the  sand 
about  this  spot  was  well  adapted  to  the  manufacture  of  glass, 
and  probably  the  glass-houses  of  Tyre  and  Sidon  were  supplied 
thence  with  this  material,  which  may  have  given  rise  to  the 
tradition. 


CHAP.  I. 


HISTORICAL  NOTICES. 


109 


That  the  ancient  Egyptians  were  well  acquainted  with  the 
method  of  making  glass  cannot  be  doubted.  The  beads  where¬ 
with  some  mummies  are  adorned,  although  composed  of  earth¬ 
enware,  have  an  external  covering  of  glaze,  which  is  true 
glass  covered  with  a  metallic  oxide;  and  recent  searchers 
have  discovered  among  the  tombs  at  Thebes  some  pieces  of 
glass  of  a  blue  color,  similar  in  their  composition  to  the  glazing 
on  the  beads  just  mentioned. 

The  glass-houses  of  Alexandria  were  long  famed  for  the 
skill  and  ingenuity  displayed  by  their  workmen.  The  Romans 
were,  at  one  time,  supplied  with  a  great  part  of  their  glass 
ware  from  that  city.  A  coarse  and  impure  manufacture  of 
drinking  vessels  had  been  prosecuted  at  Rome  from  the  time 
of  Nero;  but  the  art  could  have  made  only  a  slow  progress 
notwithstanding  the  encouragement  offered  by  the  high  prices 
at  which  glass  wares  of  foreign  make  were  sold  in  the  impe¬ 
rial  city.  The  emperor  Hadrian,  while  at  Alexandria,  re¬ 
ceived  from  a  priest  some  glass  cups  of  various  colors,  which 
had  been  used  in  the  worship  of  the  temple,  and  transmitted 
them  to  Rome  as  objects  of  great  value  and  curiosity,  with  an 
injunction  that  they  should  be  used  on  festivals  and  other  great 
occasions. 

Utensils  of  glass  have  been  found  among  the  ruins  of  Hercu¬ 
laneum,  which  city  was  destroyed  in  the  reign  of  the  empe¬ 
ror  Titus,  by  the  same  eruption  of  Mount  Vesuvius  which  cost 
the  elder  Pliny  his  life.  It  does  not  appear  that  glass  was  used 
for  admitting  light  to  dwellings  in  Herculaneum,  the  largest 
houses  having  windows  made  with  a  species  of  transparent  tale. 

In  the  British  Museum  are  four  large  cinerary  urns  made  of 
green  glass,  which  have  been  pronounced  by  a  very  competent 
authority  favorable  specimens  of  the  proficiency  of  the  ancients 
in  the  art  of  glass-blowing.  These  are  round  vases  of  an  ele¬ 
gant  form,  furnished  with  covers  and  two  double  handles.  The 
formation  of  these  handles  is,  it  is  said,  “such  as  must  convince 
any  person  capable  of  appreciating  the  difficulties  which  even 
the  modem  glass-maker  would  have  to  surmount  in  their  exe¬ 
cution,  that  the  ancients  were  well  acquainted  with  certain 
branches  of  the  manufacture.”  * 

Several  ancient  authors  ( Dion  Cassius,  Petronius  Arbiter, 
and  Isodorus)  relate,  that  in  the  reign  of  Tiberius,  an  archi¬ 
tect,  who  had  been  banished  from  Rome  on  account  of  his  great 
popularity,  having,  in  his  retirement,  discovered  the  means  of 
so  far  altering  the  nature  of  glass  as  to  render  it  malleable, 
ventured  to  return  to  Rome,  in  the  hope  of  securing  both  a  re- 


*  Memoir  on  Glass  Incrustations,  by  A.  Pellatt,  Esq. 

K 


110 


MANUFACTURE  OF  GLASS. 


CIIAP.  I. 


mission  of  his  sentence  and  a  reward  for  his  invention.  This 
discovery  not  agreeing,  however,  with  the  supposed  interests 
of  the  tyrant,  who  feared  lest  the  value  of  gold  might  be  low¬ 
ered  by  its  means,  the  architect  was  beheaded,  and  his  secret 
died  with  him.  This  is,  probably,  only  another  version  of  the 
story  related  by  Pliny,  of  the  same  important  discovery  having 
been  made  by  an  artist  in  Rome,  when  such  of  the  populace  as 
imagined  that  their  interests  would  be  injuriously  affected 
thereby  conspired  together  and  destroyed  his  dwelling. 

A  similar  discovery,  attended  by  results  as  unsatisfactory,  and 
which  is  said  to  have  occurred  in  France  in  the  more  modern 
times  of  Louis  XIII.,  is  recorded  by  Blancourt.  He  says,  that 
the  inventor  having  presented  a  bust  formed  of  malleable  glass 
to  the  cardinal  Richelieu,  was  rewarded  for  his  ingenuity  by 
perpetual  imprisonment,  lest  the  “  vested  interests”  of  French 
glass  manufacturers  might  be  injured  by  the  discovery. 

Without  venturing  altogether  to  deny  the  truth  of  these  sto¬ 
ries,  it  would  be  hard  to  subject  to  the  charge  of  presumption 
those  persons  who  entertain  doubts  upon  the  matter.  It  does 
not,  certainly,  prove  the  incorrectness  of  the  statements,  that 
no  subsequent  examiner  into  the  arcana  of  nature  has  been 
equally  fortunate  ;  and  it  is  assuredly  possible  that  some  suc¬ 
cessful  investigator  may  yet  be  the  means  of  revealing  that 
which  has  already  been  thus  ascribed  to  more  than  one  experi¬ 
menter. 

Improbable  as  the  achievement  of  this  would  seem,  it  would 
be  scarcely  more  extraordinary  than  the  transformation  of  linen 
rags  into  sugar,  or  the  conversion  of  saw-dust  into  “  wholesome, 
palatable,  and  nutritious  food.”  The  purposes  both  of  use  and 
of  ornament  to  which  glass  would  in  such  a  case  be  applied 
are  almost  endless,  and  their  importance  can  hardly  be  over¬ 
rated  ;  nor  should  we  in  these  days  have  occasion  to  fear,  lest 
the  insensate  obstructions  of  some  modern  Tiberius  or  Riche¬ 
lieu  should  step  between  the  discoverer  and  the  promulgation 
of  his  secret. 

According  to  our  present  amount  of  knowledge,  the  chance 
of  realizing  such  a  discovery  is,  however,  limited  within  the 
barest  possibility.  The  quality  of  malleability  is  in  direct  con¬ 
tradiction  to  that  of  vitrification ;  the  existence  of  the  one  state 
seems  to  be  incompatible  with  that  of  the  other.  Some  me¬ 
tallic  substances  when  greatly  urged  by  fire  are  made  to  ap¬ 
proach  towards  the  state  of  glass,  and  then  lose  their  mallea¬ 
bility  ;  a  fact  which  almost  implies  the  impossibility  of  impart¬ 
ing  the  latter  property  to  glass.  Kunkel  has  indeed  observed, 
that  it  is  possible  to  produce  a  composition  having  an  external 
glassy  appearance,  which  should  be  pliant  and  capable  of  being 


CHAP.  I. 


HISTORICAL  NOTICES. 


Ill 


wrought  under  the  hammer ;  and  Neumann  tells  us,  that  in  the 
fusion  of  muriate  of  silver  a  ductile  kind  of  glass  is  formed, 
which  may  be  moulded  or  turned  into  different  figures,  and 
which  may  be  pronounced  in  some  measure  malleable ;  facts 
to  which  Henckel  has  referred  in  order  to  account  for  the  tra¬ 
ditionary  stories  of  the  ancients. 

The  Latin  writers  of  the  Augustan  age  make  frequent  men¬ 
tion  of  glass.  Virgil  compares  to  it  the  clearness  of  the  water 
in  the  Fucine  Lake  (Ailn.  vii.  759.) ;  and  Horace  speaks  of  the 
lustre  and  transparency  of  glass  in  a  way  which  shows  that  it 
could  then  be  made  with  a  considerable  degree  of  perfection. 
In  the  year  220  a  tax  was  laid  by  Alexander  Severus  upon  the 
glass  manufacturers  of  Rome,  who  at  this  time  existed  in  such 
numbers,  that  a  principal  quarter  was  assigned  to  them  in  that 
city,  wherein  they  might  carry  on  their  processes.  This  tax 
was  still  levied  in  the  reign  of  Aurelian. 

The  most  celebrated  specimen  of  antique  glass  is  the  vase, 
which  during  more  than  two  centuries  ornamented  the  Barber- 
ina  palace,  and  which,  having  been  subsequently  purchased  by 
the  late  duchess  of  Portland,  is  better  known  in  this  country 
as  the  Portland  vase.  This  much-admired  production  was  found 
about  the  middle  of  the  sixteenth  century,  inclosed  in  a  mar¬ 
ble  sarcophagus,  and  deposited  in  the  tomb  of  Alexander  Seve¬ 
rus,  who  died  in  the  year  235.  The  body  of  this  vase,  which 
for  a  long  time  was  erroneously  supposed  to  be  formed  of  por¬ 
celain,  is  made  of  deep  blue  glass,  and  is  ornamented  with 
white  opaque  figures  in  bas-relief,  which  are  designed  and 
sculptured  in  the  style  of  cameos  with  a  degree  of  skill  which 
is  truly  admirable. 

Glass  melted  and  cast  into  plates,  is  said  by  St.  Jerome  to 
have  been  used  in  his  time  (a.  d.  422,)  to  form  windows.  About 
a  century  later,  Paulus  Silentiarius  mentions  the  windows  of 
the  church  of  St.  Sophia  at  Constantinople  which  were  covered 
with  glass ;  and  from  this  period  frequent  allusions  to  the  simi¬ 
lar  use  of  glass  are  met  with  in  various  authors. 

Long  before  the  establishment  of  the  manufacture  within 
this  island,  glass  was  known  and  used  in  England.  The  Vene¬ 
tians  who  traded  with  this  country  in  very  remote  times  fur¬ 
nished  this  among  other  articles  of  commerce  in  exchange  for 
tin.  The  erudite  Pennant  is  of  opinion,  that  glass-making  in 
Britain  dates  prior  to  the  Roman  invasion.  The  Druids  were 
accustomed  to  impose  upon  their  more  ignorant  followers  by 
means  of  clumsily-formed  beads  of  colored  glass,  which  they 
pretended  were  endued  with  the  quality  of  guarding  their  pos¬ 
sessors  from  evil. 

The  venerable  Bede,  who  lived  very  near  the  time,  and  who 


112 


MANUFACTURE  OF  GLASS. 


CHAP.  I. 


therefore  had  good  opportunities  for  ascertaining  the  fact,  has 
asserted  in  his  history  of  Weremouth,  that  in  the  year  674  the 
abbot  Benedict  sent  for  artists  from  beyond  seas  to  glaze  the 
windows  of  the  church  and  monastery  of  Weremouth  in  Dur¬ 
ham,  and  that  these  men  were  our  first  instructors  in  the  art 
of  making  window-glass.  This  art,  however,  took  root  but 
slowly  amotig  us ;  and  it  was  not  until  the  eleventh  century 
that  glass  windows  were  at  all  commonly  used,  either  in  pri¬ 
vate  dwellings  or  in  public  and  religious  edifices.  Previously 
to  this  time,  light  was  imperfectly  transmitted  through  linen 
cloths  or  wooden  lattices.  The  houses  of  the  commoner  people 
were  not,  indeed,  furnished  with  this  luxury  until  the  thirteenth 
and  fourteenth  centuries,  in  which  respect  our  ancestors  were 
greatly  behind  the  inhabitants  of  Italy  and  France. 

The  following  curious  entry,  extracted  from  the  Northum¬ 
berland  household  book,  makes  it  apparent  that  at  a  much  later 
period  than  the  one  just  mentioned,  the  comfort  of  glazed  win¬ 
dows  was  not  considered  as  a  matter  of  course  even  in  estab¬ 
lishments  where  great  state  and  magnificence  were  maintained. 
This  entry  occurs  in  the  minutes  of  a  survey  of  Alnwick  Cas¬ 
tle  made  in  the  year  1567 : — 

“And  because  throwe  extream  windes  the  glasses  of  the 
windowes  of  this  and  other  my  lords  castels  and  houses  here  in 
the  country  dooth  decay  and  waste,  yt  were  good  the  whole 
leightes  of  everie  windowe  at  the  departure  of  his  lordshippe 
f  om  lyinge  at  anie  of  his  sade  castels  and  houses,  and  dowring 
the  time  of  his  lordshippes  absence  or  others  lyinge  in  them 
were  taken  doune  and  lade  up  in  safetie ;  and  at  sooch  tyme  as 
ether  his  lordshippe  or  anie  other  sholde  lye  at  anie  of  the  sade 
places,  the  same  might  then  be  set  uppe  of  newe  with  smale 
charges  to  his  lordshippe;  whereas  now  the  decaye  thereof 
shall  be  verie  costlie  and  chargeable  to  be  repayred.” 

We  learn  also  from  Ray’s  Itinerary  (p.  187),  that  “in  Scot¬ 
land,  as  late  as  1661,  the  window’s  of  the  ordinary  country 
houses  were  not  glazed,  and  only  the  upper  parts  of  those  of 
even  the  king’s  palaces  had  glass,  the  lower  ones  having  only 
two  wooden  shutters  to  open  at  pleasure  and  admit  the  fresh  air.” 

When  desirous  in  former  times  of  giving  encouragement  to 
some  important  manufactures,  the  government  of  France  was 
induced  to  declare  their  prosecution  to  be  nowise  incompatible 
with  the  dignity  of  aristocratic  blood.  Early  in  the  fourteenth 
century  that  government  made  a  concession  in  favor  of  glass¬ 
making  greatly  beyond  this  point,  decreeing,  not  only  that  no 
derogation  from  nobility  should  follow  the  practice  of  the  art, 
but  that  none  save  gentlemen,  or  the  sons  of  noblemen,  should 
venture  to  engage  in  any  of  its  branches,  even  as  working  ar- 


CHAP.  I.  HISTORICAL  NOTICES.  118 

tisans.  This  restriction  was  accompanied  by  the  grant  of  a  royal 
charter  of  incorporation  conveying  various  important  privileges, 
under  which  the  occupation  became  eventually  a  source  of 
great  wealth  to  several  families  of  distinction,  whose  descend¬ 
ants  have  at  times  attained  to  some  of  the  highest  dignities  of 
the  state. 

The  good  policy  is  apparent  of  thus  holding  forth  induce¬ 
ments  to  the  only  parties  then  qualified  by  the  possession  of 
capital,  and  probably  also  by  their  intelligence,  to  establish 
works  upon  a  scale  that  could  lead  either  to  national  advantage 
or  individual  profit.  A  middle  class  of  persons,  springing  from 
the  lower  orders,  have  since  gradually  placed  themselves  at 
least  upon  a  level  in  point  of  intelligence  with  those  of  more 
illustrious  descent ;  and  by  the  exercise  of  that  intelligence, 
conjointly  with  prudence,  have  acquired  the  means  for  under¬ 
taking  works  of  magnitude.  This  altered  state  of  society 
would  render  such  exclusive  privileges  not  merely  unnecessary, 
biit  would  make  them  absolutely  pernicious. 

Notwithstanding  the  marked  encouragement  just  related  on 
the  part  of  the  French  government,  some  time  elapsed  before 
the  manufactures  of  France  could  rival  those  of  Italy.  Venice, 
in  particular,  long  excelled  in  the  quality  of  its  mirrors  and 
drinking-glasses,  with  which  the  manufacturers  of  that  city 
supplied  the  rest  of  Europe.  The  most  considerable  of  their 
glass-houses  were  established  at  Murano,  a  village  situated  a 
short  distance  from  the  city. 

During  the  ministry  of  the  celebrated  Colbert,  some  French 
artists,  who  while  residing  in  the  Venetian  state  had  acquired 
a  knowledge  of  the  processes  used  at  Murano  for  the  making 
of  plate  glass,  returned  to  France  in  the  hope  of  profitably  pur¬ 
suing  the  manufacture  in  their  native  country.  Such  an  event 
falling  in  with  the  views  of  Monsieur  Colbert,  who  wTas  anxious 
by  every  means  to  extend  the  useful  arts  within  the  kingdom, 
these  artists  were  in  the  year  1605  established  with  privileges 
at  Tourlaville  near  Cherbourg,  and  an  advance  of  money  was 
made  to  them  from  the  public  coffers  to  assist  in  the  formation 
of  their  establishment.  The  plates  made  by  this  company  were 
blown,  after  the  system  used  in  the  Venetian  manufactories. 

It  was  not  until  1688  that  the  beautiful  art  of  casting  plates 
of  glass  was  invented  by  a  manufacturer  named  Thevart,  who, 
obtaining  a  patent  for  the  invention  to  continue  in  force  during 
thirty  years,  established  a  company  and  erected  works  in  Paris, 
where  plates  were  cast  of  the  then  extraordinary  dimensions 
of  eighty-four  inches  long  by  fifty  inches  wide,  a  size  which 
excited  universal  astonishment  and  admiration.  The  expense 
of  conducting  such  a  manufactory  in  the  metropolis  was,  how- 

K  2 


114 


MANUFACTURE  OF  GLASS. 


CHAP.  I. 


ever,  so  great,  that  the  establishment  was  transferred  to  St 
Gobain  in  Picardy,  where  the  undertaking  was  prosecuted,  not 
without  considerable  opposition  from  the  more  ancient  asso¬ 
ciation. 

To  accommodate  the  disputes  between  these  rival  establish¬ 
ments,  Thevart’s  company  was  bound  not  to  cast  any  plates 
whose  dimensions  should  be  less  than  sixty  inches  in  length 
and  forty  inches  in  breadth.  The  largest  piece  that  had  then 
been  produced  by  blowing  did  not  exceed  fifly  inches  in  its 
largest  dimension.  This  arrangement  failed  to  produce  har¬ 
mony  between  the  rivals  ;  but  in  1695  that  end  was  effectually 
answered  by  uniting  both  companies  under  the  same  charter — 
not  however,  as  the  issue  proved,  to  their  mutual  advantage ; 
— for,  possibly  owing  to  the  want  of  the  salutary  spur  of  com¬ 
petition,  the  company  declined  in  prosperity  with  such  rapidity, 
that  in  two  years  from  the  junction  the  united  body  was  in  a 
state  of  insolvency,  obliged  to  discharge  most  of  its  workmen, 
and  to  abandon  many  of  its  furnaces. 

No  blame  can  be  charged  upon  the  French  government  for 
the  protection  and  privileges  afforded  to  these  companies.  It 
is  probable  that  without  some  immunities  neither  of  the  estab¬ 
lishments  could  at  that  early  period  have  been  undertaken. 
The  instances  however  are  rare,  and  the  circumstances  whereby 
they  have  been  attended  peculiar,  in  which  joint-stock  trading 
companies  have  been  prosecuted  to  advantage.  The  causes  of 
this  fact  are  not  difficult  of  explanation.  It  is  seldom  that  the 
personal  interest  of  those  to  whom  the  particular  management 
is  intrusted  is  sufficiently  strong  to  insure  the  requisite  amount 
of  attention,  or  the  proper  degree  of  pecuniary  watchfulness, 
if  even  the  still  more  unfavorable  condition  does  not  arise 
wherein  private  advantage  is  opposed  to  the  general  prosper¬ 
ity,  and  it  is  sought  to  conduct  the  operations  rather  with  a 
view  to  individual  profit  than  to  the  common  advantage. 

In  the  following  year  a  new  association  was  formed  out  of 
the  ruins  of  the  old  company,  under  the  management  of  An¬ 
toine  d’Agincourt,  who  re-engaged  the  discharged  workmen, 
and  by  the  prudence  of  his  arrangements  conducted  the  affairs 
with  considerable  profit  to  the  adventurers. 

Blancourt,  in  his  “Art  de  la  Verrerie,”  relates  as  the  mode 
in  which  the  casting  of  plates  of  glass  was  discovered,  that  a 
person  who  was  melting  some  of  this  material  in  a  crucible  ac¬ 
cidentally  spilt  it  while  fluid  upon  the  ground.  The  metal  ran 
under  one  of  the  large  flag-stones  wherewith  the  place  was 
paved,  which  obliged  the  workman  to  take  up  the  stone  in  order 
to  recover  the  glass.  He  then  found  it  in  the  form  of  a  plate, 
such  as  could  not  be  produced  by  the  ordinary  process  of  blow- 


CHAP.  I. 


HISTORICAL  NOTICES.  H5 

mg.  The  man’s  attention  being  roused  by  this  fact,  he  was  un- 
abie  to  sleep;  and  conceiving  at  once  the  superiority  of  this 
method  for  forming  mirrors,  he  immediately  commenced  exper- 
lmentmg  ;  and  before  the  day  appeared  had  proved  the  practi¬ 
cability  of  the  improvement  which  the  purest  chance  had  thus 
placed  within  the  sphere  of  his  observation.  This  occurrence 
is  said  to  have  arisen  200  years  before  it  was  related  by  Blan- 
court,  whose  treatise  is  dated  in  1698.  It  cannot  therefore  have 

Tbevart'renCe  t0  ^ien  recent  proposals  and  performance  of 

The  manufacture  of  flint  glass  was  first  begun  in  England  in 
the  year  1557,  at  Savoy  House  in  the  Strand,  and  in  Crutched 
P  nars.  In  1635  Sir  Robert  Mansell  obtained  a  monopoly  for 
making  this  kind  of  glass,  in  consideration  of  his  being  the  first 
person  who  employed  pit-coal  instead  of  wood  in  his  furnaces. 
1  lie  art  could  not  at  this  time  have  reached  any  great  decree 
of  perfection,  as  permission  was  further  conveyed  by  the  patent 
of  importing  drinking  glasses  of  fine  quality  from  Venice,  and 
another  half  century  elapsed  before  this  country  became  inde¬ 
pendent  of  foreign  supply  for  such  articles. 

The  second  duke  of  Buckingham  has  the  merit  of  much  im¬ 
proving  the  manufacture  of  British  glass  by  means  of  certain 
\  enetian  artists  whom  he  brought  to  London  in  1670.  Three 
years  later  than  this  period,  the  first  plates  of  English  glass 
were  made  at  Lambeth  under  the  auspices  of  the  same  noble¬ 
man.  The  violence  of  party  spirit  which  characterized  that 
age  should  lead  us  to  receive  with  caution  all  estimates  of  char¬ 
acter  which  we  may  find  recorded  by  contemporary  biographers. 
Although  there  was  unquestionably  much  of  vice  and  profligacy 
ui  the  general  conduct  of  this  favorite  of  a  vicious  and  profli¬ 
gate  master,  wTe  may  yet  hesitate  to  believe  that  the  man  who 
could  apply  himself  to  the  study  of  letters,  and  who,  in  the 
manner  above  related,  interested  himself  in  promoting  the  use¬ 
ful  arts  of  life,  could  at  the  same  time  be  so  utterly  depraved 
both  in  mind  and  in  heart  as  the  page  of  history  has  repre- 
sciitcd* 

The  first  English  establishment  of  magnitude  for  the  casting 
af  plate  glass  was  undertaken  in  1773.  A  respectable  body  of 
gentlemen  at  that  time  obtained  a  royal  charter  of  incorpora¬ 
tion,  the  privileges  of  which  were  confirmed  to  them  by  act  of 
3fjjameat>  un^er  the  style  of  “  The  Governor  and  Company 
if  British  Cast  Plate  Glass  Manufacturers;”  and  having  sub- 
bribed  a  capital  or  joint  stock  in  eighty  shares  of  five  hundred 
xiunds  eaeh,  constructed  works  of  considerable  extent  at  Ra- 
/enhead,  near  Prescot,  in  Lancashire.  This  undertaking,  the 
>nly  one  of  the  kind  existing  in  this  country.vand  rivalled  by 


116  MANUFACTURE  OF  GLASS.  CHAP.  I. 

none  but  that  of  St.  Gobain  in  France,  is  still  prosecuted  with 
success ;  and  some  description  of  its  operations  will  be  found  in 
a  future  chapter  of  this  volume. 

It  is  deserving  of  remark  that  the  Chinese,  whose  early  pro¬ 
ficiency  in  the  sister  art  of  manufacturing  porcelain  was  so 
long  unrivalled  in  Europe,  have  yet  no  practical  knowledge  of 
glass  making,  and  that  even  now  there  does  not  exist,  though- 
out  that  extensive  empire,  a  single  glass-house  which  is  proper¬ 
ly  deserving  of  that  name.  Glass  working  is  indeed  practised 
at  Canton  ;  but  the  art  is  there  wholly  confined  to  the  remanu¬ 
facture  of  old  or  broken  glass  of  foreign  make,  which  is  melted 
and  either  blown  or  moulded  into  new  forms. 

A  similar  remark  may  be  applied  to  the  inhabitants  of  Hin- 
dostan.  Dr.  Tennant  informs  us  that  “  before  the  arrival  of  the 
Europeans,  there  was  not  a  house  in  all  India  furnished  with 
glass  windows,”*  although  there  are  not  many  climates  where¬ 
in  such  an  employment  of  glass  is  more  conducive  to  comfort 
The  knowledge  which  the  Hindus  then  possessed  of  the  art  of 
making  this  material  was  limited  to  the  manufacture  of  trinkets 
and  trifling  ornaments ;  in  fact,  their  inability  to  construct  fur¬ 
naces  of  power  sufficient  to  melt  together  the  ingredients  of 
which  it  should  be  composed  rendered  it  impossible  for  that 
people  to  apply  themselves  to  the  manufacture  for  any  more 
useful  purpose.  “  Of  its  adaptation  to  optical  purposes  they 
were  so  ignorant,  as  to  be  astonished  and  confounded  at  the  ef¬ 
fects  of  a  common  spy-glass.  ”f 

Any  more  minute  inquiries  into  the  origin  and  progress  of 
the  manufacture  of  glass  would  not  offer  much  either  of  inter¬ 
est  or  advantage.  The  investigation  would  not  connect  itself 
with  any  facts  that  bear  upon  the  history  of  commerce,  nor 
throw  any  light  upon  questions  of  international  policy.  The 
general  abundance  of  materials  needful  for  making  glass,  and 
the  facility  with  which  these  can  be  converted — at  least  into 
articles  fitted  for  common  use — are  opposed  to  its  becoming 
under  any  circumstances  an  object  of  great  moment  in  foreign 
commerce.  The  advantage  possessed  by  this  country  in  the 
superior  quality  and  abundance  of  its  fuel  does  not  offer  suffi¬ 
cient  compensation  for  the  heavy  charges  that  would  attend  the 
transport  of  such  bulky  articles  to  countries  which  themselves 
possess  adequate  means  for  prosecuting  the  manufacture. 

Glass-making,  in  its  various  divisions,  has  long  proved  a  very 
considerable  branch  of  industry  in  this  kingdom ;  and  although, 
for  reasons  that  will  be  noticed,  our  continually  growing  pow- 


*  Indian  Recreations,  vol.  i.  p.  325. 

t  Mill’s  History  of  Brit.  India,  vol.  i.  p.  361.  Quarto  edition. 


CHAT.  I.  HISTORICAL  NOTICES.  117 

er  of  attaining  comforts  has  not  occasioned  a  corresponding  in¬ 
crease  in  the  quantity  retained  for  domestic  use,  our  colonial 
relations  have  always  insured  a  very  considerable  export  trade 
to  the  manufacturers. 

The  portion  of  glass  made  in  Great  Britain,  and  retained  for 
home  sale,  has  long  been  converted  into  a  source  of  considerable 
national  revenue.  If  articles  of  domestic  manufacture  are  at 
all  legitimate  objects  of  taxation,  it  does  not  appear  that  any 
peculiar  objection  can  be  advanced  against  the  extension  of  the 
system  to  this  particular  branch  of  national  industry.  The  prices 
of  such  glass  utensils  as  are  of  most  common  employment  can¬ 
not  be  considered  great  when  viewed  with  reference  to  their 
beauty  and  the  extreme  convenience  which  attends  upon  their 
use ;  while  upon  articles  of  a  more  costly  description  the  duty 
comprises  a  comparatively  small  part  of  the  price.  It  would 
lierefore  seem  little  likely  that  any  material  check  to  the  use 
d  either  description  would  be  caused  by  even  a  considerable 
Pigmentation  of  the  rate  of  duty.  The  result  has,  however, 
ilways  disproved  the  correctness  of  such  an  opinion,  as  every 
iddition  which  has  been  made  to  the  rate  of  duty  has  occasion¬ 
ed  a  most  important  falling  off  in  the  produce  of  our  glass- 
louses. 

In  the  year  1812  an  additional  duty  was  imposed  upon  glass 
nanufactures  generally,  which,  it  was  estimated  by  the  then 
hancellor  of  the  Exchequer,  would  produce  an  augmentation 
if  revenue  to  the  extent  of  328,000/.  The  immediate  conse¬ 
quences,  however,  of  this  measure,  so  far  disappointed  the  ex- 
>ectations  of  the  minister  as  to  occasion  a  falling  off  in  the 
inantity  manufactured  throughout  the  kingdom  of  rather  more 
han  one  third,  by  which  means  the  anticipated  increase  of  rev¬ 
alue  fell  short  by  the  sum  of  183,000/. 

The  general  evil  tendency  of  this  system  of  taxation  cannot, 
perhaps,  be  better  or  more  clearly  exemplified  than  by  the 
tatement  of  a  few  simple  facts  connected  with  the  manufacture 
f  glass. 

!  The  average  quantity  of  all  descriptions  annually  retained 
)r  home  use  in  the  three  years  ending  in  1793  was  373,782 
wt.,  while  the  average  quantity  consumed  during  the  three 
|  ears  ending  in  1829,  amounted  to  364,156  cwt. ;  showing  an 
jnnual  decrease  in  the  manufacture  of 9626  cwt.,  notwithstanding 
'ie  great  increase  of  population  and  the  still  greater  strides  in 
Civilization  made  during  the  interval  by  all  classes  of  the  com- 
lunity. 

If  the  quantities  produced  during  equal  periods  of  three  years, 
nmediately  preceding  and  following  the  last  and  most  consid- 
rable  advance  in  the  rate  of  duty,  are  then  contrasted  with 


118  MANUFACTURE  OF  GLASS.  CHAP.  I. 

each  other,  the  effect  appears  in  a  yet  more  striking  point  of 
view.  The  annual  average  quantity  made  for  home  use  during 
the  three  years  ending  in  1812  was  413,414  cwt.,  while  the 
average  of  the  three  following  years  ending  in  1815  was  264,931 
cwt.;  showing  an  immediate  falling  off  of  148,483  cwt.,  being 
upwards  of  35  per  cent,  upon  the  larger  quantity ;  a  circum¬ 
stance  which  could  not  fail,  among  other  evils,  to  bring  dis¬ 
tress  and  misery  upon  a  considerable  number  of  operative  man-' 
ufacturers.  * 

On  the  other  hand,  a  diminution  in  the  rate  of  duty  on  plate 
glass  was  effected  on  the  5th  of  July,  1819,  it  being  then  low¬ 
ered  from  98-s.  to  60s.  per  cwt.  As  a  consequence,  the  quan¬ 
tity  manufactured  has  since  been  steadily  and  progressively  in¬ 
creasing.  During  the  three  years  preceding  the  abatement,, 
the  average  quantity  annually  manufactured  was  6209  cwt.,i 
yielding  a  gross  revenue  of  30,424Z.,  whereas  the  average  quan¬ 
tity  made  during  the  three  years  ending  in  1829  amounted  to 
15,235  cwt.,  and  the  revenue  produced  was  45,705Z.,  being  an 
increase  of  more  than  50  per  cent.,  derived  from  a  rate  of  duty 
diminished  to  the  extent  of  40  per  cent. 

Could  any  facts  more  forcibly  point  out  the  pernicious  ten¬ 
dency  of  heavy  duties  upon  articles  of  domestic  manufacture,  of 
more  clearly  indicate  the  course  which  it  were  wise  to  follow 
in  remodelling  to  as  great  an  extent,  and  as  quickly  as  is  prac¬ 
ticable,  this  branch  of  our  financial  system  1 

It  is  much  to  be  regretted  that  any  circumstances  should  have 
arisen  to  delay  the  execution  of  the  expressed  intention  of  the! 
government  altogether  to  remove  the  duties  upon  glass.  When¬ 
ever  this  measure  shall  be  accomplished,  it  can  hardly  fail  tc 
induce  such  an  extension  of  the  manufacture  as  will  prove  gen¬ 
erally  beneficial  to  the  community.  The  abolition  of  these  du-i 
ties  would  be  accompanied  by  the  still  further  advantage  of  re-! 
moving  all  those  vexatious  regulations  and  restrictions  under1 
which  the  manufacture  is  now  carried  on,  and  which  will  cease,1 
as  a  matter  of  course,  when  the  article  is  no  longer  an  objectj 
of  revenue. 

It  is  principally  owing  to  these  restrictions  that  so  much  for-i 
eign  glass  is  now  brought  into  this  country  in  the  face  of  what 
may  be  considered  an  amply  protecting  duty.  Foreign  manu¬ 
facturers  are  allowed  to  make  any  and  every  article  out  of  that 
quality  of  glass  which  will  most  cheaply  and  advantageously 
answer  the  end,  while  our  own  artists  are  forbidden  to  form 
certain  objects,  except  with  more  costly  materials,  which  pay 
the  higher  rates  of  duty.  Nor  is  this  restriction  only  commer¬ 
cially  wrong,  since  it  forms  matter  of  just  complaint  on  the  part 
of  chemists,  that  they  are  unable  to  procure  utensils  fitted  for 


ihap.  ii. 


INGREDIENTS  OF  GLASS. 


119 


dfecting  many  of  the  nicer  operations  connected  with  their 
cience,  because  the  due  protection  of  the  revenue  is  thought 
o  require  that  such  utensils  shall  be  formed  out  of  that  quality 
f  glass  alone  winch,  apart  from  all  considerations  of  price,  is 
therwise,  from  its  properties,  really  unfitted  for  the  purpose, 
relaxations  are,  indeed,  sometimes  made  on  this  head  in  par- 
icular  cases  by  the  commissioners  of  Excise;  but  the  trouble 
ecessanly  attending  applications  to  a  public  board  is  greater 
ian  can  be  compensated  by  the  trifling  money  advantage  that 
an  result  m  each  case  to  the  manufacturer,  and  the  interests  of 
nence  are,  consequently,  made  to  suffer. 


CHAP.  II. 


N  THE  VARIOUS  INGREDIENTS  EMPLOYED  IN  MAKING 

GLASS. 


ass  always  ccmp^ed  °f  Silex  with  Alkali.-Different  Descriptions  of 
Gla»s.— Sea-Sand.— Soda  and  Potash.— Pearl-Ash.— Barilla.— Kelp.— Wood 
Chafk  ^ltre‘  Ijlt^larSe-  Minium. — Manganese. — Arsenic. — Borax. — 


Under  the  general  name  of  glass,  chemists  comprehend  all 
ineral  substances,  which,  on  the  application  of  heat,  pass 
rough  a  state  of  fusion  into  hard  and  brittle  masses,  and  which, 
then  broken,  exhibit  a  lustrous  fracture.  Most  glasses  are 
insparent  also ;  and  the  non-existence  of  this  property  is  gen- 
ally  owing  to  the  presence  of  some  foreign  and  unessential 
bstance. 

The  glass  of  commerce— that  beautiful  manufacture  to  which 
3  generic  name  is  most  commonly  applied— does  not  include 
wide  a  range  of  bodies  ;  and  is  always  composed  of  some  si- 
ious  earth,  the  fusion  and  vitrification  of  which  has  been  oc- 
uoned  by  certain  alkaline  earths,  or  salts,  and  sometimes  with 
i  aid  of  metallic  oxides. 

There  are  five  different  and  distinct  qualities  of  glass  manu- 
tured  for  domestic  purposes ;  viz. 

Flint  glass,  or  crystal ; 

Crown  or  German  sheet  glass ; 

Broad  or  common  window  glass 
Bottle  or  common  green  glass ;  and 
Plate  glass ; 

materials  and  the  processes  used  in  making  which  form  the 
)ect  of  our  present  inquiry. 

tefbre  commencing  the  description  of  any  of  the  manipula- 
is  employed  in  this  interesting  manufacture,  it  will  be  better 


GLASS  MANUFACTURE. 


CHAP.  II. 


120 


to  give  a  general  account  of  the  different  materials  used,  and  to 
point  out  how  the  particular  qualities  of  glass  are  influenced  by 
the  properties  of  those  various  ingredients. 

Each  of  the  five  descriptions  contains,  in  common  with  the 
others,  two  ingredients,  which,  indeed,  are  essential  to  theii 
formation — silex  and  an  alkali. 

The  variations  of  quality,  and  distinctive  differences  observ¬ 
able  in  glass,  principally  result  from  the  kind  of  alkali  employ¬ 
ed,  and  its  degree  of  purity,  as  well  as  from  the  addition  of 
other  accessory  materials ;  such  as  nitre,  oxide  of  lead  or  of 
manganese,  white  oxide  of  arsenic,  borax,  or  chalk. 

Silex  is  not  equally  proper  in  all  its  forms  for  the  composi 
tion  of  glass.  Sea  sand,  which  consists  of  spherical  grains  ol 
quartz,  so  minute,  as  to  be  qualified  for  the  purpose  withou 
any  preparation  except  careful  washing,  is  the  form  whereii 
silex  is  most  commonly  used  for  the  purpose  in  England.  A1 
sea  sand  is  not,  indeed,  equally  applicable  to  the  glass-maker 
purpose.  That  used  in  this  country  for  making  the  finer  de 
scriptions  of  ware  is  usually  obtained,  either  from  the  port  o 
Lynn,  in  Norfolk,  or  from  Alum  Bay,  on  the  western  coast  o 
the  Isle  of  Wight. 

The  best  glass  was  formerly  made  with  common  flints,  ca 
cined  and  ground  in  the  manner  already  described,  as  used  i 
the  manufacture  of  pottery,  and  hence  the  name  which  it  a< 
quired  of  flint  glass.  The  employment  of  silex  in  this  form 
now  wholly  discontinued  in  glass-houses,  as  it  is  known  th; 
some  qualities  of  sand  answer  the  purpose  equally  well,  whii 
the  labor  and  expense  of  calcining  and  grinding  are  saved  t 
the  substitution. 

Both  soda  and  potash  are  well  adapted  to  the  purpose  of  ni: 
king  glass.  They  are  used  in  the  form  of  carbonates ;  that  ij 
holding  carbonic  acid  in  combination  with  themselves  as  base 
The  acid  flies  off  during  the  progress  of  the  manufacture,  ar 
the  result  is  a  compound  of  silex  and  alkali. 

As  already  stated,  the  quality  of  glass  is  influenced  by  tl 
degree  of  purity  of  the  alkali.  For  making  the  finest  flii 
glass,  pearl-ash,  which  is  potash  in  a  purer  form,  must  be  use 
The  alkali  must  previously  be  still  further  purified  by  solutif 
and  subsidence,  and  then  evaporating  the  fluid  to  dryness.  I 
this  purification  a  loss  is  sustained,  amounting  to  between  !i 
and  40  per  cent,  in  the  weight  of  pearl-ash.  Coarser  kinds  <| 
alkali,  such  as  barilla,  kelp,  or  wood-ashes,  which  are  combin 
with  many  impurities,  are  employed  for  the  production  of  inf 
rior  glass.  Complete  fusion  and  vitrification  are  accomplish 
by  these  means,  the  impurities  even  being  of  a  nature  to  ass 
towards  the  production  of  these  effects.  The  green  color  ii 
parted  to  glass,  is  produced  by  the  iron,  which  is  present  in 


CHAP.  II. 


INGREDIENTS  OF  GLASS. 


121 


greater  or  less  degree  in  these  courser  alkaline  substances. 
Barilla,  when  sufficiently  cheap,  is  always  chosen  preferably  to 
wood-ashes  or  kelp.  The  recent  abatement  of  the  import  duty 
levied  upon  this  article  of  commerce  will,  therefore,  probably 
tend  to  the  increased  consumption  of  barilla  in  glass-houses. 

A  very  small  proportion  of  nitre  is  used  in  the  composition 
of  glass,  to  occasion  the  destruction  of  any  carbonaceous  mat¬ 
ter  which  may  exist  in  the  ingredients.  This  salt  must  be 
added  previous  to  the  fusion  of  the  glass.  Ata  degree  of  heat 
much  below  that  of  the  furnace,  nitre  will  decompose,  giving 
out  much  oxygen,  and  maintaining  such  metallic  oxides  as 
may  be  present  in  their  highest  state  of  oxygenation.  It  is 
thus  of  use  in  fixing  arsenic,  the  volatile  property  of  which  in¬ 
creases  as  it  approaches  the  metallic  state. 

Oxide  of  lead,  in  the  form  of  either  litharge  or  minium,  is 
essential  to  the  making  of  flint-glass,  into  the  composition  of 
which  it  enters  very  largely.  This  metal  acts,  in  the  first 
place,  as  a  most  powerful  flux,  promoting  the  fusion  of  all  vit- 
rifiable  substances  at  comparatively  low  temperatures.  It  is 
also  permanently  beneficial  in  imparting  highly  valuable  prop¬ 
erties  to  the  glass  of  which  it  forms  a  part.  This,  by  its  means, 
is  rendered  much  more  dense ;  has  a  greater  power  of  refract¬ 
ing  rays  of  light ;  possesses  more  tenacity  when  red-hot,  caus¬ 
ing  it  for  that  reason  to  be  more  easily  worked ;  and  is  render¬ 
ed  more  capable  of  bearing  uninjured  sudden  changes  of  tem¬ 
perature.  On  the  other  hand,  glass,  into  the  composition  of 
which  much  lead  has  entered,  is  so  soft  as  to  be  easily  scratch¬ 
ed  and  injured  if  rubbed  against  hard  bodies.  Such  glass  is 
also  improper  as  a  recipient  for  many  fluids  which  are  of  an 
acrid  nature,  by  which  it  would  be  corroded  and  destroyed. 
Another  great  inconvenience  attending  the  use  of  lead  is  this, 
that  it  does  not  become  intimately  enough  united  with  the 
other  components  for  the  whole  mass  to  assume  an  uniform 
density.  It  will  almost  always  happen,  that  the  glass  at  the 
bottom  of  the  pot  contains  a  larger  proportion  of  litharge  than 
that  above.  This  inequality  of  density  is  continually  increas¬ 
ing  as  the  contents  of  the  pot  are  diminished  by  the  workman ; 
and  it  is  thence  impossible  to  withdraw  from  it  any  two  por¬ 
tions  whose  densities  shall  agree.* 


*  Mr.  Faraday  has  stated,  in  his  paper  on  the  manufacture  of  glass  for  op. 
tical  purposes,  which  appeared  in  the  Philosophical  Transactions  for  1830, 
that  he  found,  on  examining  “pots  containing  glass  not  more  than  six 
inches  in  depth,  made  from  the  usual  materials,  and  retained  at  a  full  heat 
for  twenty-four  hours,”  the  following  differences  of  specific  gravity  be¬ 
tween  the  glass  taken  from  the  bottom  and  surface  of  the  pots : — 

Top,  -  3  38  3  30  328  321  3  15  373  385  381  3  31  330 
Bottom,  4  04  3  77  385  3  52  3-80  4  63  474  475  399  3  74 

L 


122  GLASS  MANUFACTURE.  CHAP.  II. 

Monsieur  Guyton  Morveau  has  related  a  very  curious  exem¬ 
plification  of  this  fact,  which  once  occurred  to  himself  when 
experimenting  in  conjunction  with  Monsieur  de  Buffon  in  the 
plate-glass  manufactory  near  Langres.*  Remaining  in  the  cru¬ 
cible  was  a  portion  of  flint  glass  in  fusion,  composed  of  thirty- 
two  parts  powdered  crystal,  thirty-two  parts  minium,  sixteen 
of  soda,  and  one  part  nitre.  To  this  was  added  the  requisite 
quantity  of  the  ingredients  commonly  employed  for  forming 
plate-glass  in  the  manufactory,  and  the  whole  was  melted  to¬ 
gether  in  the  furnace.  When  the  mass  was  sufficiently  refined 
it  was  laded  into  the  cistern,  cast  on  the  copper  table  in  the 
usual  manner,  and  transferred  to  the  annealing  furnace.  Its 
quality  being  subsequently  submitted  to  examination,  the  plate 
was  found  to  be  composed  of  two  distinct  and  perfectly  level 
strata  through  the  whole  mass,  the  lower  stratum  occupying 
about  one  third  of  its  thickness. 

So  complete  an  instance  of  the  precipitation  of  the  denser 
through  the  lighter  portion  is  not  elsewhere  to  be  met  with  in 
the  records  of  glass-making :  its  occurrence  in  this  particular 
occasion  should  probably  be  referred  to  the  active  agency  of 
some  cause  which  escaped  the  observation  of  the  two  philoso¬ 
phers. 

It  is  a  general  effect  of  this  inequality,  that  the  glass,  when 
wrought,  appears  waved ;  a  defect  which  is  particularly  incon¬ 
venient  in  that  which  is  intended  for  the  construction  of  opti¬ 
cal  instruments.  Glass  is  also  fusible  at  lower  temperatures 
according  to  the  proportion  of  lead  which  it  contains.  This 
quality,  which  would  be  mischievous  for  some  purposes,  is,  on 
the  contrary,  beneficial  for  others.  It  is  often  essential  to 
chemists  that  they  shall  be  able,  during  the  progress  of  their 
experiments,  to  bend  the  tubes  with  which  they  are  operating. 

Black  oxide  of  manganese  has  long  been  used  for  clearing 
glass  from  any  foul  color  which  it  might  accidentally  possess 
through  the  impurity  of  the  alkali  employed,  and  in  particular 
from  that  green  tinge  which  marks  the  presence  of  iron.  This 
property  of  manganese,  when  in  the  form  of  an  oxide,  occa¬ 
sioned  it  to  be  anciently  known  as  glass  soap ,  a  name  which 
very  accurately  describes  its  use.  The  circumstances  attend¬ 
ing  the  employment  of  this  substance  in  glass-making  are  of 
rather  a  curious  nature.  When  added  in  a  moderate  propor¬ 
tion  to  any  simple  glass,  it  imparts  a  purple  color ;  and  should 
its  quantity  be  much  increased,  this  color  is  deepened  until  the 
glass  becomes  nearly  black.  If,  while  the  mass  thus  colored  is 
still  in  fusion,  either  white  arsenic,  or  charcoal,  or  other  carbo¬ 
naceous  matter  be  added,  an  effervescence  is  seen  to  follow, 


*  Ann.  ile  Chim.  vol.  lxxiii.  p.  113. 


CHAP.  II. 


INGREDIENTS  OF  GLASS. 


123 

and  the  color  becomes  gradually  more  faint  until  it  altogether 
disappears,  and  the  glass  is  rendered  clear  and  transparent. 
Provided  the  green  hue  which  it  is  desired  to  counteract  be 
considerable,  the  application  of  a  very  small  quantity  of  manga¬ 
nese  is  not  followed  by  any  sensible  tinge  of  purple ;  but  the 
moment  that  the  proportion  is  more  than  sufficient  for  the  pur¬ 
pose,  this  color  immediately  appears,  and  must  be  corrected. 
This  correction  is  performed  in  a  very  simple  manner  in  the 
glass-house,  by  thrusting  into  the  pot  of  melted  glass  a  piece  of 
wood,  which,  becoming  charred  by  the  heat,  causes  the  purple 
again  to  vanish;  while  a  slight  effervescence  as  before  de¬ 
scribed,  and  the  escape  of  numerous  bubbles  of  air,  are  plainly 
perceptible.  If  nitre  be  then  added,  the  purple  color  will  be 
restored. 

The  reason  fos,  these  changes  it  is  not  difficult  to  explain. 
The  oxide  of  manganese  imparts  a  purple  color,  only  when  in  a 
state  of  high  oxygenation.  When  brought  into  contact  with 
carbonaceous  matter,  it  is  partially  deprived  of  its  oxygen,  and 
loses  its  coloring  property.  The  air-bubbles  which  escape  con¬ 
sist  of  carbonic  acid  gas,  which  is  disengaged  by  the  action  of 
the  charcoal  on  the  oxide  of  manganese.  The  effect  which 
follows  upon  the  introduction  of  nitre  is  of  a  contrary  nature. 
When  made  of  a  red  heat  this  substance  gives  out  oxygen  in 
great  abundance,  and  the  manganese  being  thus  reinvested  with 
the  oxygen  of  which  it  was  deprived  by  the  charcoal,  resumes 
with  it  the  coloring  property. 

Another  advantage  attending  the  use  of  oxide  of  manganese 
results  from  its  property  of  powerfully  assisting  in  the  fusion  of 
earthy  bodies.  It  also  gives  considerable  density  to  glass,  but 
the  same  disadvantage  accompanies  its  use  as  already  has  been 
noticed  with  regard  to  litharge.  Having  from  its  greater  spe¬ 
cific  gravity  a  tendency  to  settle  towards  the  bottom  of  the  pot, 
the  glass  by  this  means  varies  in  density  throughout  its  sub¬ 
stance,  in  addition  to  which  circumstance  the  manganese  acts 
injuriously  upon  the  pots  by  corroding  them  at  the  bottom. 

One  of  the  uses  of  white  oxide  of  arsenic  has  already  been 
described,  that,  namely,  of  correcting  the  coloring  effects  of 
manganese.  It  is  also  a  very  powerful  flux,  and  a  great  tempt¬ 
ation  to  its  use  is  found  in  its  cheapness.  It  should,  however, 
be  employed  with  moderation.  If  a  considerable  time  be  not 
allowed  for  its  intimate  incorporation  with  the  other  ingredients 
of  the  glass,  this  will  appear  clouded  or  milky ;  a  fault  which 
will  afterwards  increase  with  the  lapse  of  time.  An  excessive 
quantity  of  arsenic  likewise  occasions  the  glass  to  become  grad¬ 
ually  soft  and  to  decompose,  for  which  reason  the  employment 
of  drinking-vessels  in  this  condition  is  unsafe. 


124  GLASS  MANUFACTURE.  CHAP.  II. 

Another,  and  a  harmless,  application  of  arsenic  in  glass¬ 
making  is,  when  it  is  introduced  into  the  fused  mass  in  order  to 
dissipate  any  carbonaceous  matters  which  result  from  defects 
in  preparing  the  alkali.  In  this  case,  small  lumps  of  white  ar¬ 
senic  are  intimately  blended  with  the  mass  by  stirring.  The 
great  heat  causes  it  at  once  to  unite  with  and  to  carry  off  the 
carbon  in  a  volatile  form,  leaving  the  glass  entirely  free  from 
carbonaceous  matter,  and  nearly  so  from  arsenic. 

Borax  is  used  in  preparing  only  the  finest  descriptions  of 
glass :  its  employment  is,  indeed,  principally  confined  to  plate 
glass.  It  is  too  expensive  to  admit  of  its  forming  part  in  the 
composition  of  common  descriptions,  although  its  use  in  all 
cases  would  be  desirable,  as  its  efficacy  in  promoting  the  fusion 
of  vitrifiable  substances  is  unrivalled.  When  the  borax  has  been 
introduced,  the  compound  is  caused  by  it  to  flow  with  great 
freedom,  and  to  be  without  specks  and  bubbles,  which  would 
impair  both  its  beauty  and  utility.  Should  the  alkali  employed 
prove  deficient  in  strength,  a  small  portion  of  this  salt  will  serve 
as  an  effectual  remedy. 

Lime  in  the  form  of  chalk  is  useful  as  a  very  cheap  flux.  It 
is  also  beneficial  in  facilitating  the  operations  of  the  workman 
in  fashioning  glass,  and  it  has  the  property  of  diminishing  its 
liability  to  crack  on  exposure  to  sudden  and  great  variations  of 
temperature.  Chalk  can  only  be  used  sparingly,  however,  in 
the  glass-house,  as  the  escape  of  carbonic  acid  causes  the  in¬ 
gredients  in  the  pot  to  swell  considerably  during  the  fusion. 
The  presence  of  lime  in  any  excessive  degree  would  also  occa¬ 
sion  the  rapid  destruction  of  the  pots,  upon  the  substance  of 
which  it  acts  with  considerable  energy.  Glass  wherein  lime 
exists  in  excess  is  also  rendered  cloudy,  although  the  mass  while 
in  fusion  appears  perfectly  pellucid.  Not  more  than  about  six 
per  cent,  of  lime  can  be  added  without  risking  this  defect. 


CHAP.  III. 


FURNACES. 


125 


CHAP.  HI. 

ON  THE  CONSTRUCTION  OF  FURNACES,  ETC. 

Stability  of  Furnace  Essential.— Fritting  Furnace,  or  Calcar.— Its  Use.— 
Working  Furnace.— Double  Furnace.— Proportionate  Dimensions  of  Fur- 
n ace  and  Pots.— Wood-Furnaces.— Comparative  Consumption  of  Fuel  in 
Wood  and  Coal  Furnaces.— Annealing  Oven.— Lier-Pans.— Glass-Pots.— 
Their  Formation  and  Seasoning. 

It  is  essential  to  the  well  conducting  of  the  operations  of 
glass-houses  that  their  furnaces  should  be  well  and  substantially 
built  of  the  best  materials,  and  according  to  the  most  approved 
construction. 

Monsieur  Loysel  was  so  deeply  impressed  with  the  necessity 
of  devoting  the  greatest  degree  of  attention  to  this  branch  of 
the  art,  that  nearly  one  half  of  his  clever  treatise  “  Sur  l’Art  de 
la  Verrerie”  is  occupied  with  its  details.  This  author  not  only 
gives  instructions  for  the  choice  of  materials  proper  for  con¬ 
structing  crucibles  and  furnaces ;  but  also  points  out  the  forms 
which  will  be  found  most  convenient  and  advantageous. 

In  this  country,  and  since  the  appearance  of  the  work  of  M. 
Loysel,  those  operations  connected  with  the  useful  arts  which 
depend  upon  the  agency  of  heat  have  become  much  better  un¬ 
derstood  than  formerly,  so  that  principles  for  the  right  attain¬ 
ment  of  which  it  was  then  necessary  for  individuals  to  search 
and  inquire,  and  frequently  even  to  experiment,  are  now  be¬ 
come  matters  of  every-day  practice.  It  cannot,  therefore,  be 
necessary  to  imitate  that  author  in  all  his  lengthened  initiatory 
directions  for  the  digging  and  purifying  of  clay — in  his  descrip¬ 
tion  of  the  qualities  that  should  determine  our  selection  of  this 
material,  or  in  the  detail  of  mechanical  arrangements  that  will 
prove  most  efficacious  in  giving  durability  to  furnaces.*  All 
these  particulars  may  safely  be  committed  to  the  skilfulness  of 
the  professional  builder. 

Some  other  points  there  are,  however,  connected  with  this 
subject,  wherein  a  greater  degree  of  knowledge  than  is  at 
present  possessed  is  indeed  desirable.  To  persons  who  have  be¬ 
stowed  the  smallest  attention  upon  the  phenomena  of  heat  and 
combustion  it  can  scarcely  fail  to  appear  that  science  has  yet  an 


*  In  stating  the  degrees  of  consistence  of  the  clay  most  proper  for  the  fur¬ 
naces  in  different  parts  and  stages  of  their  construction,  Mr.  Loysel  points 
out  a  simple  method  of  ascertaining  the  attainments  of  these  degrees,  which 
has  the  advantage  of  being  easily  accomplished  by  any  workman.  It  consists 
in  dropping  a  leaden  ball  of  a  given  weight  from  a  determinate  height  upon 
the  mass,  which  should  be  of  that  density  which  will  allow  the  ball,  by  the 
force  of  gravitation  acquired  in  its  descent,  exactly  to  bury  itself  in  the  clay. 


126  GLASS  MANUFACTURE.  CHAP.  III. 

ample  field  for  research  there  open  to  her  investigations,  and 
that  the  arts  have  still  to  look  for  further  and  most  important 
benefits  at  the  hand  of  philosophy. 

The  whole  operations  of  the  glass-house  depend  upon  the  sta¬ 
bility  of  its  furnaces.  In  their  original  structure  the  prudent 
manufacturer  will,  therefore,  not  hesitate  to  avail  himself  of  the 
assistance  of  the  ablest  builders,  and  to  employ  materials  which 
are  best  qualified  by  their  density  and  infusibility  for  resisting 
the  action  of  violent  and  long-continued  heat.  No  present  sa¬ 
ving  in  the  cost  of  construction  can  at  all  compensate  for  the 
expense  and  interruptions  occasioned  by  the  necessity  for  fre¬ 
quent  repairs,  and  still  less  for  the  losses  of  time,  labor,  and  ma¬ 
terials,  that  would  accompany  casualties,  the  chances  of  which 
would  be  multiplied  by  want  of  proper  attention  to  the  matters 
here  pointed  out.  An  equal,  and  perhaps  even  a  greater  degree 
of  judgment  is  required  for  the  selection  of  materials  proper  to 
form  glass-pots  or  crucibles,  since  these  have  to  withstand  the 
action  of  heat  in  as  violent  a  degree  as  any  part  of  the  furnace, 
and  are  additionally  exposed  to  injury  from  the  solvent  property 
possessed  by  some  of  the  materials,  for  the  fusion  of  which  they 
are  employed.  These  pots  are  therefore  made  of  the  most  re¬ 
fractory,  that  is,  the  least  fusible,  materials,  and  are  fashioned 
with  every  possible  attention  to  their  strength. 

Three  different  kinds  of  furnaces  are  employed  in  the  manu¬ 
facture  of  glass.  One,  which  is  called  the  calcar,  a  name  cor¬ 
rupted  from  the  French  word  calquaise,  is  used  for  that  calci¬ 
nation  of  the  materials  to  which  they  must  be  subjected  previ¬ 
ously  to  their  complete  fusion  and  vitrification.  This  process, 
which  is  called  fritting,  a  term  likewise  borrowed  from  the 
French,  is  used  for  various  reasons.  In  the  first  place,  it  expels 
all  moisture  from  the  materials,  the  presence  of  which  would 
hazard  the  destruction  of  the  glass-pots.  Next  it  drives  of£ 
either  wholly  or  in  great  part,  the  carbonic  acid  gas  from  the 
chalk  and  alkalies  employed,  by  which  means  the  swelling  of 
ingredients  in  the  pots  is  either  prevented,  or  moderated  within 
safe  limits.  This  calcination  has  the  further  advantage  of  de¬ 
stroying  all  carbonaceous  matters  that  may  be  present  in  the 
materials.  But  the  principal  object  of  previous  calcination  is, 
that  a  chemical  union  may  be  effected,  or  at  least  commenced, 
between  the  silex,  the  alkali,  and  the  metallic  oxides.  Other¬ 
wise,  at  the  heat  of  the  working  furnace,  the  alkali  would  fuse, 
and  its  comparative  levity  would  cause  it  to  take  its  station  at 
the  surface,  while  the  other  ingredients  would  subside  towards 
the  bottom.  The  uncombined  alkali  would,  in  this  case,  after 
acting  upon  and  injuring  the  substance  of  the  crucibles,  be,  in 
great  part,  volatilized  and  lost;  and  a  portion  of  the  sand  would 


CHAP.  III. 


FURNACES. 


127 


remain  unvitrified,  while  the  glass  actually  produced  would 
contain  an  excessive  quantity  of  silica. 

These  observations  do  not  apply  to  the  preparation  of  mate¬ 
rials  for  making  flint  glass,  the  fusibility  of  which  is  much 
greater  than  that  of  other  descriptions,  owing  to  the  presence 
of  its  large  proportion  of  lead.  For  this  reason,  manufacturers 
of  this  kind  of  glass  apply  the  process  of  calcination  to  the  sand 
alone,  with  the  view  of  separating  from  it  all  carbonaceous  im¬ 
purities,  previous  to  its  admixture  with  the  remaining  materials. 

The  name  of  fixed  alkalies  has  been  given  to  soda  and  pot¬ 
ash  to  denote  their  property  of  resisting  the  destructive  influ¬ 
ence  of  fire.  As  they  are  volatilized  freely  by  subjection  to  a 
red  heat,  this  property  cannot,  however,  be  strictly  ascribed  to 
either  of  these  substances,  and  the  title  must  be  understood  only 
as  distinguishing  them  from  other  alkaline  bodies,  which  are 
acted  upon  by  comparatively  low  additions  of  temperature. 

The  calcar  is  in  the  form  of  an  oven  about  ten  feet  long, 
seven  feet  wide,  and  two  feet  high.  The  coal  used  in  heating 
it  is  placed  in  a  sort  of  trough  on  one  side,  and  the  flame  is 
made  to  reverberate  from  the  crown  of  the  oven  back  to  the 
frit.  In  this  operation,  care  is  required  to  keep  the  degree  of 
heat  at  all  times  within  that  which  would  melt  the  materials, 
and  at  first  below  the  point  whereat  the  yet  uncombined  alkali 
would  be  volatilized. 

The  process  must  not  be  hurried  at  first ;  but  after  two  or 
three  hours  the  temperature  may  be  gradually  raised  until  the 
mass  becomes  pasty.  Having  been  kept  in  this  state  during 
three  or  four  hours  longer,  it  is  then  removed  from  the  calcar 
and  cut  quickly,  before  it  has  time  to  harden,  into  square  cakes. 
These  are  piled  away  for  future  use.  It  is  the  opinion  of  many 
glass-makers  that  frit  is  improved  in  quality  by  age ;  under 
which  impression  some  among  them  so  manage  their  operations 
as  not  to  bring  their  store  successively  to  use  until  it  has  been 
prepared  for  at  least  twelve  months. 

The  working  furnace  is  that  wherein  the  frit,  when  placed 
in  the  glass-pots  or  crucibles,  is  fully  melted  and  converted  into 
glass.  These  crucibles  are  deep  pots,  varying  in  size  according 
to  the  objects  of  the  manufacturer,  but  sometimes  large  enough 
for  each  to  contain  a  ton  weight  of  glass.  Twelve  of  these  are 
usually  placed,  at  regular  intervals,  in  the  circumference  of 
each  kiln,  their  only  opening  being  at  the  side  nearest  to  the 
wall  of  the  kiln,  in  which  they  meet  with  corresponding  open¬ 
ings,  so  that  the  pots  can  be  readily  charged,  and  their  contents 
is  readily  removed,  by  the  workmen  who  stand  in  recesses 
formed  by  projections  of  the  masonry.  The  external  form  of  the 
furnace  is  circular,  rising  conically  from  its  base  and  termina- 


GLASS  MANUFACTURE. 


CHAP.  III. 


128 

ting  in  a  chimney.  The  interior  is  dome-shaped,  and  supported 
on  arches.  Flues  are  constructed  under  these  for  the  admis¬ 
sion  of  atmospheric  air,  which,  rising  through  the  fire-bars  that 
occupy  the  centre  of  the  floor  of  the  furnace,  the  flame  and 
heated  air  are  made  to  envelop  the  pots,  and  thence  pass  on  to 
the  chimney  issuing  from  the  centre  of  the  dome. 

A  very  important  saving  in  the  article  of  fuel  has  lately  been 
effected  in  one  of  the  London  glass-houses,  that  of  Messrs.  Pel- 
latt  and  Co.,  by  substituting  for  one  of  the  large  twelve-pot  fur¬ 
naces  they  had  been  accustomed  to  use  two  similarly  construct¬ 
ed,  but  having  only  one  half  the  diameter.  The  circumference 
of  these  two  being  together  equal  to  that  of  the  large  furnace, 
they  are  made  to  contain  as  great  a  number  of  pots,  and  of  the 
same  size,  as  were  formerly  employed ;  while  the  internal  area 
of  the  two,  being  together  equal  to  only  one  half  that  of  the  fur¬ 
nace  for  which  they  are  substituted,  the  pots  are  necessarily 
brought  more  than  before  within  the  intensest  influence  of  the 
fire.  The  same  chimney  is  made  to  serve  for  both  furnaces,  by 
which  means  the  expense  attending  the  alteration  has  been 
much  diminished. 


Fig.  1. 


It  is  said,  that  the  weekly  expenditure  of  coals  has  been 
lessened,  by  means  of  this  alteration,  to  the  extent  of  ten  chal¬ 
drons. 

The  dimensions  of  the  crucibles  and  furnace  should  bear 
some  relation  to  each  other.  If  the  former,  from  their  diminu¬ 
tive  size,  are  much  below  the  efficiency  of  the  furnace,  a  very 
needless  expenditure  of  fuel  will  be  the  result ;  and  should  the 


CHAP.  III.  FURNACES.  129 

crucibles  be  too  large  for  the  power  of  the  kiln,  the  heat  will 
not  prove  sufficient.  In  this  case,  an  excess  of  fluxing  materi¬ 
als  must  be  used  in  order  to  form  glass,  which  will  be  imper¬ 
fect,  according  as  it  is  fused  below  the  most  beneficial  degree 
of  temperature.  The  relative  proportions  of  pots  and  furnace 
may  be  somewhat  varied  according  to  the  power  of  promoting 
combustion,  which  partly  depends  upon  construction  and  situa¬ 
tion.  Loysel  recommends,  that  in  general  the  aggregate  area 
of  the  crucibles  should  be  very  little  beyond  one  fourth  of  the 
area  of  the  furnace.  The  experience  whereon  this  recommend¬ 
ation  rested  was  drawn  from  the  use  of  wood  as  a  combusti¬ 
ble,  which  requires  a  greater  space  than  coal  for  the  develop¬ 
ment  of  a  given  effect.  The  difference  thus  arising  would,  on 
the  other  hand,  be  lessened  by  the  necessity  which  we  are 
under  for  covering  the  pots ;  whereas,  if  the  kiln  is  heated  by 
means  of  wood,  these  may  remain  uncovered,  and  their  con¬ 
tents  will,  in  consequence,  be  more  efficiently  acted  on  by  the 
heat.  Loysel  states,*  as  the  result  of  experiments  continued 
during  a  whole  year,  that  the  weight  of  dry  beach  wood  con¬ 
sumed  in  a  glass-house  furnace  exceeded  the  weight  of  coal 
burnt  in  the  same  furnace,  and  during  an  equal  period,  in  the 
proportion  of  45  to  28.  According  to  Lavoisier,  the  heating  ef¬ 
fects  of  wood  and  coal  are  in  the  proportion  of  1089  to  600. 

The  result  of  Loysel’s  experiment  should  consequently  have 
6hown  similar  effects  from  the  combustion  of  45  parts  by  weight 
of  wood,  and  24-8  parts  of  coal ;  the  difference  between  this 
last  quantity  and  28  being,  probably,  the  loss  consequent  upon 
covering  the  crucibles. 

The  openings  already  mentioned,  as  serving  for  the  introduc¬ 
tion  of  the  materials  into  the  crucibles,  and  for  the  removal  of 
the  melted  glass,  are  called  boccas.  These  may  be  closed  either 
wholly  or  partially,  according  to  the  need  of  the  workman,  by 
means  of  movable  collars,  or,  to  speak  more  correctly,  by  tem¬ 
porary  screens  made  of  fire-clay.  On  either  side  of  each  bocca 
is  a  smaller  circular  opening,  sometimes  called  a  boccarella, 
but  more  generally  by  the  familiar  name  of  nose-hole,  the  par¬ 
ticular  use  of  which  will  be  explained  hereafter. 

The  annealing  oven,  or  lier,  is  a  long,  low,  rectangular  cham¬ 
ber,  heated  at  one  end,  and  furnished  with  numerous  shallow 
iron  trays,  which  can  be  passed  easily  along  the  level  bottom 
of  the  chamber.  These  trays  are  called  lier-pans,  or  fraiches  ; 
which  names,  together  with  those  of  several  implements  used 
in  glass-houses,  are  evidently  adopted  from  the  French. 

As  regards  the  structure  of  the  annealing  chamber,  there  is 
nothing  that  particularly  requires  notice,  or  that  will  not  be 


*  L’Art  de  la  Verrerie,  p.  72. 


130 


GLASS  MANUFACTURE. 


CHAP.  III. 


rendered  sufficiently  clear  by  the  explanation  of  its  use  that 
will  be  given  in  the  following  chapter,  while  describing,  in 
their  regular  course,  the  consecutive  processes  of  the  manufac¬ 
ture. 

Every  glass-house  should  possess  within  itself  the  means  of 
making  all  the  crucibles  and  other  earthen  utensils  that  may 
be  required  for  its  operations.  The  conveyance  of  these  from 
any  considerable  distance  would  add  materially  to  their  cost, 
not  only  by  the  mere  expense  of  carriage,  but  through  the 
greater  liability  to  fracture,  whereto  such  unwieldy  vessels 
would  in  that  case  be  subject. 

These  crucibles,  or  glass-pots,  should  be  made  with  five  parts 
of  the  best  Stourbridge  fire-clay  and  one  part  of  old  broken 
crucibles  ground  to  powder  for  that  purpose.  Great  nicety  is 
required  in  mixing  these  ingredients  and  in  working  them  to¬ 
gether,  in  order  to  drive  out  from  their  substance  every  particle 
•  of  air,  the  presence  of  which  would,  by  its  expansion  in  the  fur¬ 
nace,  occasion  the  immediate  breaking  of  the  pots. 

The  method  invariably  pursued  for  kneading  the  clay  is, 
Fig.  2.  that  the  workman  treads  on  it  for  a  consid¬ 
erable  time  with  his  naked  feet,  turning  it 
over  from  time  to  time,  so  that  every  part 
may,  in  its  turn,  be  subjected  to  the  required 
pressure.  An  attempt  was  recently  made  by 
a  glass  manufacturer  to  employ  machinery 
for  the  purpose ;  but  after  having  incurred 
considerable  expense,  and  exerted  much  in¬ 
genuity  in  perfecting  his  apparatus,  this  gen¬ 
tleman  has  reverted  to  the  old  inartificial  method,  as  being  deci¬ 
dedly  the  best  calculated  to  insure  the  goodness  of  his  crucibles. 
This  attempt  at  improvement  was  not  relinquished,  until  the 
losses  which  were  sustained  in  its  prosecution  became  of  seri¬ 
ous  moment. 

After  the  crucibles  are  formed,  they  are  suffered  to  remain 
for  a  considerable  time  in  the  apartment  wherein  they  were 
made,  in  order  that  they  may  dry  equally  throughout  their  sub¬ 
stance.  It  is  not,  indeed,  considered  prudent  to  remove  them 
from  this  situation  until  they  shall  have  been  formed  for  at  least 
a  twelvemonth. 

For  some  little  time  before  a  pot  is  put  to  use,  it  must  be 
placed  in  an  apartment  wherein  heat  can  be  artificially  admit¬ 
ted,  and  either  raised  or  lowered  at  pleasure.  It  is  then  re¬ 
moved  for  about  three  days  to  a  furnace  particularly  appro¬ 
priated  to  the  baking  of  pots ;  and  here  the  temperature,  which 
at  first  is  moderate,  is  gradually  increased,  until  at  last  it  is 


CHAP.  IV. 


FLINT  GLASS. 


131 


made  nearly  as  intense  as  that  of  the  working  furnace,  for  in¬ 
sertion  in  which  the  crucible  is  then  sufficiently  fitted. 

With  all  the  skill  and  care  that  can  be  employed  in  their 
manufacture,  these  crucibles  will  frequently  break  during  a 
very  early  period  of  their  use,  and  the  loss  occasioned  by  that 
means  to  the  manufacturer  is  in  many  ways  one  of  very  seri¬ 
ous  importance. 


CHAPTER  IV. 

ON  THE  MANUFACTURE  OF  FLINT  GLASS. 

The  most  beautiful  and  costly  Kind  of  Glass.— Importance  of  its  Quality  for 
Optical  Purposes.— Experiments  for  its  Improvement— Undertaken  by  the 
Royal  Society— Promoted  by  Government.— Distinguishing  Properties  of 
Flint  Glass. — To  what  owing. — Different  Compositions. — Process  of  Melt¬ 
ing.— Glass-Gall. — Its  Use. — Curious  Phenomenon.— Implements. — Col¬ 
lecting  Glass  on  Rod. — Marver. — Paraison. — Blowing. — Re  heating. — 
Elongating. — Pontil. — Fashioning. — Detaching. — Removal  to  Annealing 
Oven.— Moulding.— Annealing.— Why  indispensable.— Bologna  Phials. — 
Rupert’s  Drops. 

Flint  glass — known  in  foreign  countries  under  the  name  of 
crystal — retains  among  us  the  title  originally  imparted  by  its 
principal  ingredient,  although  the  use  of  flint  in  its  composition 
has  long  since  been  discontinued. 

This  glass  is  the  beautiful  and  peculiarly  refulgent  com¬ 
pound  whereof  the  finest  articles  designed  for  domestic  use 
or  for  ornament  are  made.  Of  all  the  vitrified  compounds 
that  are  manufactured,  it  is  the  heaviest  and  the  most  brilliant ; 
the  one  most  easily  fashioned  by  the  hand  of  the  workman,  and 
that  which  has  the  greatest  refractive  power.  It  is  also,  from 
the  nature  of  its  constituent  materials,  the  most  costly. 

Vessels  of  flint  glass  cannot,  however,  be  properly  applied  to 
ill  purposes.  If|  for  instance,  they  are  used  to  contain  car¬ 
bonate  of  ammonia,  they  will  very  soon  become  so  exceedingly 
brittle,  that  the  very  slightest  apparent  cause  will  occasion 
aieces  to  fall  out.  Common  green  bottle  glass  is  not  liable  to 
liis  objection. 

Were  we  to  judge  from  the  practice  of  different  manufac¬ 
turers,  in  bringing  together  the  ingredients  that  form  this  com¬ 
pound,  we  must  believe,  that  to  adhere  to  any  exact  proportions 
s  by  no  means  indispensable.  In  almost  every  different  glass- 
louse  a  peculiar  recipe  is  followed,  and  no  two  writers  upon 
he  subject  agree  in  their  statement  of  the  exact  doses  wherein 
my  of  its  components  should  be  used.  It  is  by  no  means  be- 
ieved,  however,  that  these  vague  proceedings  are  without  in- 
:onvenience,  or  that  some  particular  compound  might  not  be 


GLASS  MANUFACTURE. 


CHAP.  IV. 


132 


discovered  and  adopted,  which,  for  many  purposes,  would  be 
superior  to  every  other. 

The  employment  of  this  species  of  glass  in  the  construction 
of  optical  instruments  renders  every  attempt  towards  its  im¬ 
provement  a  matter  of  universal  interest  and  importance.  A 
committee  of  scientific  men  have  been  for  some  years  engaged, 
at  the  expense  of  government,  in  a  series  of  experiments,  with 
a  view  to  discover  some  composition  by  which  glass  may  be 
obtained  in  large  pieces,  free  from  those  defects  which  have 
hitherto  circumscribed  the  power  of  telescopes  within  a  nar¬ 
row  limit.  In  such  investigations,  however,  great  difficulties 
are  to  be  encountered ;  and  a  long  time  is  as  necessary  as  great 
talents  to  overcome  them.  The  progress  which  has  been  made 
by  the  committee,  though  not  perhaps  so  great  as  the  lovers 
of  science  could  have  wished,  is  still  as  great  as  the  difficulties 
of  the  subject — even  in  the  most  able  hands — would  have  led 
us  to  hope  for,  and  is  sufficient  to  justify  sanguine  anticipations 
of  future  success. 

The  properties  of  flint  glass  which  distinguish  it  from  other 
vitrified  substances  are  owing  to  the  presence  of  some  metallic 
oxide.  All  metals,  when  oxidated,  will  combine  with  silica 
and  alkali  to  form  glass.  Few  of  them  are,  however,  properly 
qualified  for  the  purpose,  in  consequence  of  their  imparting 
colors  to  the  mass.  The  oxides  of  lead  and  of  bismuth  are  the 
only  two  which  may  be  used  in  sufficient  quantity  without  pro¬ 
ducing  this  inconvenience  ;  and  as  lead  is  by  much  the  cheap¬ 
est  of  these  metals,  it  is  always  preferably  employed  in  the 
manufacture.  An  over  dose  of  lead  will,  indeed,  discolor  glass, 
imparting  to  it  a  tinge  of  yellow. 

It  is  essential  to  the  goodness  of  the  glass  that  no  impurities 
or  foreign  matters  should  be  combined  with  the  lead,  and  as 
the  adulteration  of  its  various  oxides  is  both  easily  effected,  and 
difficult  of  detection,  the  glass-maker  who  does  not  prepare 
this  substance  for  himself,  should  make  his  purchases  only  from 
persons  on  whose  probity  he  can  rely.  Loysel  recommends 
the  use  of  minium ,  as  being  less  susceptible  of  adulteration 
than  the  other  oxides  of  lead.  English  glass-makers  more  fre¬ 
quently  employ  litharge. 

The  author  just  mentioned  gives  as  the  composition  of  crys¬ 
tal,  where  coal  is  employed  as  fuel, — 


White  sand . 100  parts. 

Red  lead .  80  to  85 

Pearl-ash .  35  to  40 

Nitre . 2  to  3 

Oxide  of  manganese . 0-6 


Where  wood  is  used  for  the  reduction  of  the  ingredients,  and 


CHAP.  IV.  FLINT  GLASS.  133 

where  consequently,  the  crucibles  may  be  left  uncovered  du¬ 
ring  the  process,  a  different  mixture  is  preferred.  In  this,  a 
much  smaller  proportion  of  metallic  oxide  is  added ;  and  the 
reason  assigned  by  M.  Loysel  for  this  variance  is,  that  the  air, 
having  constant  and  unimpeded  access  to  the  surface  of  the 
glass,  supplies  any  deficiency  of  oxygen,  while  the  process  is, 
through  the  more  direct  application  of  heat,  more  quickly  per¬ 
formed,  and  the  glass  when  manufactured  is  harder  and  more 
durable.  The  proportions  given  for  this  compound  are, — 

White  sand . 100  parts. 

Red  lead  .  50  to  60 

Pearl-ash  . 30  to  40 

Oxide  of  arsenic .  0-75  to  1 

The  specific  gravity  of  this  glass  will  not  be  so  great  as  that 
of  the  former  compound  in  the  proportion  of  29  to  32,  and  its 
refractive  power  will  evidently  be  smaller  also. 

Messrs.  Aikin,  who,  as  a  matter  of  scientific  research, 
formerly  directed  their  minds  to  the  consideration  of  this  im¬ 
portant  branch  of  manufacture,  and  who  then  made  many  ex¬ 
periments  connected  with  the  art  of  glass-making,  state*  that  a 
very  excellent  article  may  be  made  from — 

120  parts  fine  clean  white  sand  ; 

40 - well  purified  pearl-ash ; 

35 - litharge  or  minium ; 

13 - nitre,  and  a  small  quantity  of  the  black 

oxide  of  manganese ; 

■he  superior  fluxing  power  of  the  nitre  supplying,  in  that 
■espect,  the  difference  which  exists  in  the  proportion  of  lead 
tetween  this  compound  and  the  first  formula  of  Loysel.  To 
ntroduce  so  large  a  dose  of  metallic  oxide  as  is  recommended 
>y  the  French  author  produces  an  inconveniently  soft  material, 
fhat  the  proportion  is  excessive  may  well  be  inferred  from  the 
act  ascertained  by  Dr.  Priestley,  that  if  a  tube  of  glass  so  com- 
'ounded  be  made  red-hot,  and  a  stream  of  hydrogen  gas  be 
iassed  through  it,  the  whole  inner  surface  will  be  covered  with 
half  brilliant  black  substance,  which  results  from  a  partial 
eduction  of  the  lead,  and  moisture  will  appear  at  the  further 
nd  of  the  tube. 

The  result  of  many  preliminary  experiments  made  on  a  re- 
ent  occasion  by  Mr.  Faraday,  with  the  object  of  producing  per- 
ictly  homogeneous  glass  for  optical  purposes,  induced  that  gen- 
eman  to  give  the  preference  to  a  compound  of  silica,  boracic 
cid,  and  oxide  of  lead,  brought  together  in  single  proportionals, 
nd  which  he  therefore  designates  a  silicated  borate  of  lead. 


*  Dictionary  of  Chemistry,  vol.  i.  p.  490. 

M 


134  GLAS8  MANUFACTURE.  CHAP.  IV. 

The  important  aim  of  Mr.  Faraday’s  inquiries  induced  him 
to  neglect  no  one  particular  by  which  they  could  be  forwarded, 
and  he  accordingly  employed  all  those  chemical  means  with 
which  he  is  so  perfectly  acquainted  to  insure  the  absolute  purity 
of  the  ingredients  which  he  thus  selected. 

The  oxide  of  lead  was  converted  from  the  state  of  litharge 
into  a  nitrate  by  first  washing  it  and  separating  the  carbona¬ 
ceous  and  ferruginous  particles,  and  then  placing  it  in  a  clean 
earthen  vessel,  and  dissolving  in  dilute  nitric  acid,  so  as  to  form 
a  hot  saturated  solution.  After  18  or  24  hours  the  crystals 
which  had  formed  were  collected,  broken  up  into  small  parti¬ 
cles,  and  repeatedly  washed  in  fresh  clear  portions  of  the 
mother  liquor,  in  order  to  remove  any  insoluble  deposited  mat¬ 
ter.  When  thus  perfectly  cleaned,  the  broken  crystals  were 
drained,  and  then  dried  by  being  placed  in  a  sand  bath  and 
constantly  stirred,  after  which  they  were  preserved  m  glass 
bottles  for  future  use. 

Mr.  Faraday  was  enabled  to  procure  pure  boracic  acid  in 
crystals  from  the  manufacturers,  subjecting  it  in  every  case, 
however,  to  careful  examination,  and  testing  it  by  various 
agents  to  ascertain  the  absence  of  impurities. 

Sand  from  the  coast  of  Norfolk  needed  no  other  preparation 
to  insure  its  purity  than  to  be  well  washed  and  calcined,  and 
this  was  the  only  source  whence  Mr.  Faraday  drew  his  supply 
of  silica. 

The  previous  fritting  described  in  the  last  chapter  was 
formerly  performed  for  the  manufacture  of  all  kinds  of  glass; 
but,  as  regards  the  kind  under  description,  is  not  now 
adopted.  The  materials  are  used  in  a  state  of  greater  purity, 
and  the  process  is,  on  that  account,  as  well  as  for  another 
reason  already  given,  no  longer  considered  advantageous. 

The  ingredients  having  been  intimately  mixed,  are  cast,  by 
means  of  clean  iron  shovels  through  the  side  openings,  into  the 
crucibles;  which,  previously  to  this,  must  be  brought  to  a 
white  heat.  The  pots  are  filled  at  once  with  the  mixture ; 
but  as  the  bulk  of  this  decreases  materially  in  melting,  a  fresh 
portion  must  be  added  when  this  effect  has  been  produced ;  and 
this  operation  is  repeated  until,  by  these  successive  fillings,  the 
vessels  at  length  become  fully  charged  with  melted  glass.  Be¬ 
fore  any  fresh  portion  of  materials  is  added,  that  already  in  the 
crucible  must  be  completely  melted.  When  this  is  full,  the 
opening  through  which  the  charge  was  introduced  is  materially 
lessened  with  wet  clay,  so  that  only  a  narrow  hole  remains, 
through  which  the  impurities  may  be  removed,  and  small  por¬ 
tions  of  the  contents  may,  from  time  to  time,  be  drawn  tor 
examination. 


CHAP.  IV. 


FLINT  GLASS. 


135 


Immediately  upon  the  materials  being  placed  in  the  cruci¬ 
bles,  the  heat  of  the  furnace  is  raised  to  its  highest  point.  The 
contents  are  soon  observed  to  sink  down  in  the  state  of  a  soft 
paste,  and  ere  long  become  perfectly  melted.  The  glass  does 
not,  however,  immediately  thereupon  appear  transparent,  but 
loses  its  opacity  by  slow  degrees,  as  a  white  porous  scum, 
known  by  the  name  of  sandiver  or  glass-gall,  rises  through 
the  mass  and  is  removed.  This  scum  appears  to  consist  of 
salts,  which  more  or  less  exist  in  alkalies,  and  which  salts,  hav¬ 
ing  little  or  no  affinity  for  silex,  and  being  specifically  lighter 
than  glass,  rise  to  the  top.  Another  foreign  substance  is  some¬ 
times  found  at  the  bottom  of  the  pots,  and  is  removed  when  the 
glass  is  worked  off.  This,  which  is  also  called  sandiver,  is  of 
a  nature  altogether  different  from  the  scum  before  mentioned, 
being  a  vitrified  mass  of  metallic  and  earthy  impurities.  In 
the  strong  heat  of  the  furnace  glass-gall  is  exceedingly  volatile ; 
so  that,  if  not  removed  as  it  forms  on  the  surface,  it  would  all 
be  dispersed  in  the  form  of  a  dense  vapor,  very  dark  at  first, 
and  growing  white  by  degrees,  as  the  glass  becomes  purer. 
This  vapor  is  very  corrosive,  and  acts  injuriously  upon  the  tops 
of  the  crucibles. 

Sandiver  is  purchased  by  refiners  of  metals,  who  use  it  as  a 
powerful  flux.  It  is  necessary  that  the  whole  of  this  substance 
should  come  away  before  the  glass  is  withdrawn  from  the  pots 
for  use,  otherwise  articles  formed  with  it  will  appear  cloudy, 
and  filled  with  bubbles.  A  very  strong  and  long  continued 
heat  is  generally  required  before  the  whole  impurities  are  dis¬ 
charged.  As  the  process  advances,  the  glass  proves  increas¬ 
ingly  flexible,  heavier,  and  less  brittle,  till  at  length  the  glass- 
gall  is  altogether  thrown  off,  no  more  vapors  rise,  the  bubbles 
expand,  rise  to  the  surface  and  burst,  and  the  whole  is  seen  to 
be  colorless  and  translucent. 

In  this  state,  vitrification  is  complete,  but  the  glass  is  too  fluid 
to  be  fashioned,  and  for  this  purpose  its  temperature  must  be 
lowered  by  stopping  the  draught  of  the  furnace  in  that  particu- 
1  lar  part  where  the  crucible  is  placed ;  the  clay  wherewith  its 
;  opening  was  lessened  is  then  removed,  and  the  operations  of 
1  the  glass-blower  may  be  commenced. 

When  cooled  to  the  heat  most  proper  for  its  being  wrought, 

'  the  glass  has  lost  its  perfect  fluidity,  being  of  a  consistent  and 
tenacious  mass,  soft  enough  to  yield  to  the  slightest  external 
impression,  yet  capable  of  being  bent,  pulled,  and  fashioned  into 
all  imaginable  shapes,  without  cracking  or  parting  with  its  te- 
!  nuity ;  so  that  if  in  this  state  it  be  stretched  or  drawn  out,  it  will 
preserve  the  form  of  a  solid  fibre,  constantly  decreasing  in  its 
diameter,  and  will  not  separate  until  reduced  to  the  merest  fila- 


136 


GLASS  MANUFACTURE. 


CHAP.  IV. 


ment.  When  no  longer  heated  to  redness,  glass  becomes  rigid, 
brittle,  and  transparent.  During  the  whole  time  employed  in 
working  a  pot  of  glass,  which  varies  from  five  to  twenty  hours, 
and  is  sometimes  even  longer,  its  consistence  should  be  main¬ 
tained  as  nearly  as  possible  at  the  same  point,  and  to  succeed  in 
this  calls  for  considerable  attention  on  the  part  of  the  work¬ 
men. 

The  contents  of  all  the  crucibles  do  not  come  into  the  work¬ 
ing  state  at  the  same  moment ;  but  no  injury  arises  from  this 
cause,  as  glass  may  remain  for  a  very  considerable  period  in  the 
melted  state  without,  in  any  respect,  altering  its  qualities.  The 
fusion  and  perfect  refining  of  flint  glass,  as  here  described,  are 
usually  completed  in  about  forty-eight  hours  from  the  first 
charging  of  the  crucibles. 

In  the  operations  of  a  glass-house  it  is,  indeed,  common,  pur¬ 
posely  to  manage  the  vitrifying  of  the  materials  so  that  the  con¬ 
tents  of  the  different  crucibles  shall  be  brought  to  the  state 
proper  for  blowing  in  succession,  that  when  the  glass  contained 
in  one  is  all  worked  up,  that  in  another  shall  be  in  perfect 
readiness  for  use.  By  this  arrangement  the  workmen  experi¬ 
ence  no  interruption,  and  the  heat  of  the  furnace  is  constantly 
maintained,  which  last  is  a  consideration  of  some  importance ; 
for  if  through  any  accident,  the  temperature  be  allowed  to  sink 
in  a  material  degree,  considerable  expense  of  time  and  fuel  are 
required  for  its  restoration. 

It  is  by  no  means  advisable  to  employ  in  the  formation  of  the 
same  glass  vessel  materials  drawn  from  more  than  one  cruci¬ 
ble.  Although  the  original  composition  may  have  been  alto¬ 
gether  identical,  and  the  fusion  of  all  has  been  simultaneously 
carried  forward  in  the  same  furnace,  still  a  minute  difference 
may,  and  generally  will,  exist  in  the  constituent  proportions  of 
each  mass,  arising  from  an  accidental  variance  of  draught,  and 
consequently  of  heat,  in  different  parts  of  the  furnace,  whereby 
some  crucibles  may  have  been  made  to  part  with  a  larger  pro¬ 
portion  of  their  alkali  than  others.  Any  circumstances  which 
interfere  with  the  perfect  sameness  of  quality  in  every  part  of 
vessels  formed  of  glass  renders  them  more  liable  to  break  on 
exposure  to  sudden  changes  of  temperature,  by  reason  of  their 
differing  tendencies  to  expand  and  contract  under  such  circum¬ 
stances. 

The  implements  used  by  glass-blowers  are  few  in  number, 
and  exceedingly  inartificial  in  their  form  and  construction. 
The  principal  one  is  simply  a  hollow  iron  rod  or  tube,  about 
five  feet  long,  upon  one  end  of  which  the  workman  collects  the 
quantity  of  melted  glass  that  will  suffice  for  forming  the  article 
intended.  In  this  operation  the  rod  is  dipped  into  the  pot  and 


CHAP.  IV. 


FLINT  GLASS. 


137 

turned  about  several  times.  If  the  size  of  the  vessel  requires  a 
considerable  weight  of  glass  for  its  formation,  the  rod  is  taken 

Fig.  3. 


out  and  exposed  momentarily  to  the  current  of  air,  by  which 
means  the  surface  of  the  glass  already  collected  is  sufficiently 
cooled  for  a  fresh  portion  to  adhere,  and  this  proceeding  is  re¬ 
peated  until  enough  is  collected  for  the  object. 

When  the  rod  thus  loaded  is  withdrawn  from  the  crucible,  it 
is  held  for  a  few  seconds  in  a  perpendicular  position,  the  end  to 
which  the  glass  is  attached  being  nearest  to  the  ground,  that  by 
its  own  weight  the  mass  may  be  lengthened  out  beyond  the  rod. 
The  next  operation  is  to  roll  the  glass  on  the  flat  surface  of  a 
smooth  horizontal  iron  plate  called  the  marver,  a  name  corrupt¬ 
ed  from  the  French  word  “  marbre."  By  this  means  the  par¬ 
ticles  of  glass  are  agglomerated  in  a  cylindrical  form,  which  is 
then  called  by  the  workmen  a  paraison.  The  workman  then 
applies  his  mouth  to  the  other  end  of  the  tube,  and  blows  strong¬ 
ly  through  it,  so  that  his  breath,  penetrating  the  centre  of  the 
red-hot  glass,  causes  it  to  be  distended  into  a  hollow  globe.  The 
pressure  of  the  breath  must  be  continued  upon  the  tube  for  a 
few  seconds  to  prevent  the  return  of  any  portion  of  the  air 


Fig.  4. 


through  the  tube,  otherwise  the  external  air  being  more  dense 
than  the  heated  portion  confined  within,  the  globe  would  col¬ 
lapse  :  when  it  has  been  somewhat  stiffened  by  cooling,  this 
accident  is  no  longer  to  be  apprehended. 

M  2 


138 


GLASS  MANUFACTURE. 


CHAP.  IV. 


The  globe,  which  is  not  made  sufficiently  thin  by  this  one 
blowing,  is  then  heated  anew  by  being  held  a  little  within  the 
opening  of  the  furnace ;  the  breath  is  again  employed  as  before, 
and  so  on  repeatedly,  until  the  proper  size  and  thickness  of  the 
globe  are  satisfactorily  attained. 

If  the  form  of  the  intended  vessel  requires  the  globe  to  be 
elongated,  this  effect  is  produced  by  giving  to  the  rod,  while 
the  glass  attached  to  it  is  softened  by  heat,  an  alternating  mo¬ 
tion  similar  to  that  of  a  pendulum,  or  by  dexterously  making  it 
perform  a  circle  swiftly  through  the  air.  The  tendency  to  fly 
off  from  the  centre  which  is  thus  imparted  causes  the  particles 
to  change  their  relative  positions  in  a  degree  corresponding  with 
the  amount  and  duration  of  the  force  employed. 

At  this  stage  another  implement,  called  a  punt ,  or  pontil,  is 
brought  into  use.  This  is  a  solid  iron  rod  of  a  cylindrical  form, 

Fig.  5. 


smaller  and  lighter  than  the  tube  used  for  blowing,  and  conse¬ 
quently  more  within  the  power  and  management  of  the  work¬ 
man.  Upon  one  end  of  this  rod  a  small  portion  of  melted  glass 
is  collected,  by  an  assistant,  from  the  crucible,  and  in  this  state 
is  applied  to  the  surface  of  the  globe  on  the  side  opposite  to  that 
where  it  is  already  attached  to  the  tube.  The  two  heated  sub¬ 
stances  speedily  uniting,  the  glass  is  detached  from  the  hollow 


Fig.  6. 


rod,  by  touching  it  near  to  their  point  of  contact  with  a  small 
piece  of  iron  wetted  with  cold  water.  This  occasions  the  glass 


CHAP.  IV. 


FLINT  GLASS. 


139 


-o  crack,  so  that  by  giving  a  smart  stroke  to  the  hollow  rod,  it 
:s  immediately  and  safely  separated,  leaving  a  small  hole  at  the 
point  or  rupture. 

The  workman  now  receives  from  his  attendant  the  pontil 
vitn  the  glass  vessel  attached,  and  after  reheating  it  at  the 
nrnace  mouth  as  before,  seats  himself  on  a  sort  of  stool  provided 


Fig.  7. 


mth  arms  sloping  forward,  whereon  the  pontil  is  supported  be- 
pre  him  in  a  horizontal  position,  the  glass  being  at  the  man’s 
lght  hand.  Thus  placed  he  governs  with  his  left  hand  the 
rovements  of  the  pontil  by  twirling  it  to  and  fro  along  the  arms 
r  the  stool;  and  taking  in  his  right  hand  an  iron  instrument, 
ailed  a  procello,  the  blades  of  which  are  connected  too-ether  by 
n  elastic  bow,  in  the  manner  of  a  pair 
f  sugar-longs,  he  enlarges  or  contracts 
ie  vessel  in  different  places  until  it  as- 

nnes  the  requisite  form.  Any  supera-  _ 

undance  of  material  is  cut  away  by  the  scissors  while  the 
ass  is  red-hot,  with  as  much  ease  as  they  could  be  made  to 
lvide  a  piece  of  soft  leather. 

If  the  article  is  of  a  kind,  by  its  size  or  by  the  complex  na- 
ire  ot  its  form,  to  occupy  much  time  in  its  manufacture,  it 
ust  occasionally  be  reheated,  as  its  increasing  rigidity  makes 
more  difficult  of  management. 

To  insure  the  requisite  regularity  in  shape  and  size,  the 
orkman  is  provided  with  compasses  and  a  scale  marked  off  in 
et  and  inches. 

The  finished  article  is  detached  from  the  pontil  in  the  same 
anner  as  it  has  previously  been  from  the  blowing  tube,  by 
e  ing  it  at  the  point  where  it  is  attached,  and  is  then  dropped 
'n  y  on  a  bed  of  ashes  kept  at  the  man’s  side  for  the  purpose. 


Fig.  8. 


140  GLASS  MANUFACTURE.  CHAP.  IV. 

It  is  then  taken  up  on  a  pronged  stick,  or,  when  from  its  shape 
this  mode  is  inconvenient  or  impracticable,  the  glass  is  made 
to  rest  during  the  detaching  process  on  a  wooden  shovel, 
wherein  it  consequently  remains  when  divided.  In  either  case 
a  boy  in  attendance  conveys  it  without  loss  of  time,  and  while 
yet  exceedingly  hot,  to  the  annealing  oven. 

If  it  be  required  to  give  to  the  article  any  form  or  pattern 
which  is  unattainable  by  the  simple  means  narrated,  a  mould  is 
provided,  into  which  the  glass  is  placed  while  it  is  being  blown, 
and  where  it  receives  the  requisite  impression  with  as  much  fa¬ 
cility  and  faithfulness  as  wax. 

The  process  of  annealing  is  one  of  very  great  importance ; 
without  it,  glass  would  be  liable  to  fly  with  the  smallest  change 
of  temperature,  and  would  break  with  the  merest  scratch  or 
touch,  or  even  without  any  apparent  external  cause  of  injury. 
The  most  reasonable  theory  which  has  been  proposed  in  expla¬ 
nation  of  this  disposition  in  unannealed  glass  is,  that  by  its  sud¬ 
den  cooling  the  external  particles  are  forcibly  contracted,  while 
the  inner  substance  still  remains  soft  and  expanded.  The  two 
portions  thus  take  up  positions,  in  relation  to  each  other,  very 
different  from  those  which  they  would  occupy  if  the  contraction 
of  the  whole  had  gone  forward  equally  and  gradually.  By  this 
means  a  constant  strain  is  kept  up  between  the  different  parts, 
and  should  a  force  be  applied  of  a  nature  to  rive  any  the  smallest 
portion  asunder,  the  equilibrium  of  resistance  is  deranged,  and 
the  elastic  quality  of  the  glass  causes  the  injury  to  be  felt 
strongly  and  suddenly,  but  very  unequally,  through  the  whole 
mass. 

This  theory  appears  to  receive  confirmation  from  the  well 
known  and  often  repeated  experiments  made  with  the  Bologna 
phial  and  with  Rupert’s  drops.  The  first  is  a  phial  of  ordinary 
shape  made  of  any  kind  of  glass,  much  thicker  at  its  bottom 
than  in  its  upper  portion,  and  which  has  been  suddenly  cooled 
in  the  air.  This  phial,  from  its  thickness,  will  sustain  a  con¬ 
siderable  blow  from  any  blunt  instrument,  or  will  bear  unin¬ 
jured  the  sudden  concussion  caused  by  the  fall  of  a  leaden  bul¬ 
let.  But  if  any  hard  and  angular  substance,  such  as  a  minute 
portion  of  gun  flint  or  even  a  grain  of  sand,  be  dropped  into  it, 
the  bottom  will  crack  all  round  and  drop  off.  In  performing 
this  experiment,  if  the  glass  be  very  brittle  and  the  substance 
dropt  upon  it  be  very  hard  and  sharp — a  cut  diamond  for  in¬ 
stance — this  has  been  seen  to  pass  through  the  thick  bottom 
with  apparently  as  little  resistance  as  would  be  offered  by  a 
cobweb. 

The  greater  comparative  thickness  of  the  bottom  is  an  indis¬ 
pensable  quality  of  these  Bologna  phials,  and  the  more  consid- 


CHAP.  IV. 


FLINT  CLASS. 


141 


erable  this  disproportion  is  made,  the  more  easily  will  the  dis¬ 
ruption  be  effected.  Some  of  these  vessels  have  been  struck 
by  a  wooden  mallet,  and  were  uninjured,  notwithstanding  the 
force  applied  was  sufficient  to  drive  a  nail  into  most  kinds  of 
wood  ;  and  yet  the  glasses  broke  readily  when  a  small  shiver 
of  flmt  weighing  only  two  grains  was  gently  dropt  within  them 
1  lint  being  very  hard,  and  its  angles  when  fractured  extremely 
sharp,  its  points  of  contact  with  the  glass  are  exceedinoly 
smalJ,  so  that  the  effect  produced  by  even  so  very  minute  a 
portion  of  this  substance  will  be  comparatively  greater  than 
would  accompany  the  blow  given  by  a  much  larger  but  softer 
ind  less  angular  body,  and  which  for  these  reasons  would  di¬ 
vide  the  shock  between  a  greater  comparative  number  of  parti¬ 
cles  of  the  glass. 

.  Another  theory  has  been  proposed  in  order  to  account  for  this 
singular  propeity  in  certain  forms  of  unannealed  glass.  It  has 
ieen  imagined  that  the  sudden  cooling  of  glass  may  occasion  it 
o  be  more  electric  than  is  consistent  with  the  cohesive  attrac- 
ion  of  its  particles,  and  that  the  sudden  setting'  in  motion  of 
he  electric  fluid  which  glass  contains,  may  occasion  throughout 
he  substance  a  propagation  of  the  motion  of  that  fluid,  which 
vill  go  on  accumulating  within  itself  a  force  too  great  to  be  at 
ength  resisted. 

This  theory  is  by  no  means  free  from  difficulties,  yet  it  seems 
o  derive  support  from  a  fact  which  was  developed  in  the  course 
if  some  experiments  made  before  the  Royal  Society,  in  which 
flass  vessels,  the  thick  bottoms  of  which  were  only  slightly 
ubbed  by  the  finger,  broke  after  the  interval  of  half  anliour 
pad  occurred  from  the  time  of  rubbing. 

:  Rupert’s  drops  are  small  solid  pieces  of  common  green  glass, 
vhich  have  been  dropped  while  red-hot  into  cold  water,  and’ 
phich  are  thus  caused  to  take  the  form  of  rounded  lumps  elon- 
•ated  into  a  kind  of  tail.  The  spherical  part  will  bear  very 
ough  treatment  without  injury;  but  if  the  smallest  portion  of 
be  tail  be  broken  offj  the  whole  article  instantly  bursts  into  a 
ountless  number  of  fragments,  so  minute  as  to  produce  only  a 
light  stinging  sensation  in  the  hand  by  the  sudden  disruption, 
r  one  of  these  drops  is  immersed  in  a  phial  or  tall  glass  filled 
nth  water,  and  its  end  be  broken  off  with  a  pair  of  pincers,  the 
ulb  will  be  rent  so  suddenly  and  with  so  great  a  force  as  will 
ifallibly  break  the  vessel  wherein  it  is  contained.  The  stoutest 
ine  or  beer  bottle  would  not  be  strong  enough  to  withstand 
ie  shock. 

Messrs.  Aikin  completely  destroyed  this  property  in  drops  of 
iis  kind  and  in  Bologna  phials,  by  heating  them  to  redness  and 
len  allowing  them  to  cool  gradually  as  in  the  annealing  oven. 


142  GLASS  MANUFACTURE.  CHAP.  IV. 

Not  only  was  their  quality  of  bursting  corrected  by  this  treat¬ 
ment,  but  the  particles  of  glass  were  made  to  assume  a  closer 
union  among  themselves,  which  fact  was  proved  by  the  acquire¬ 
ment  of  a  sensible  increase  in  their  specific  gravity. 

The  internal  form  of  an  annealing  oven  has  been  already  de¬ 
scribed.  Articles  newly  made  are  placed  on  the  shallow  trays 

Fig.  9. 


previously  mentioned,  in  the  part  of  the  oven  most  exposed  to 
the  heat  of  the  fire,  which,  it  will  be  remembered,  is  kindled 
under  one  end  only.  Each  one  of  these  lier  pans  or  fraiches,  as 
it  is  filled,  is  pushed  forward  in  the  oven,  towards  the  colder 
end,  to  make  place  for  a  fresh  tray,  until  the  articles,  at  length  1 
and  in  succession,  reach  the  farthest  extremity  of  the  oven, 
whence  they  are  taken,  but  little  warmer  than  the  temperature 
of  the  atmosphere. 

By  the  gradual  manner  in  which  they  have  parted  with  their 
heat,  time  lias  been  allowed  for  the  regular  contraction  of  the 
whole  into  an  uniform  and  consistent  substance. 

In  glass-houses  where  objects  of  various  magnitudes  and  de¬ 
scriptions  are  made,  two  or  more  of  these  annealing  ovens  are 
usually  attached  to  each  working  furnace.  Pieces  which  are 
large,  and  of  considerable  substance,  require  that  the  oven  in 
which  they  are  annealed  should  be  made  much  hotter  than  is 
necessary  for  thinner  and  smaller  pieces.  Glass  which  is  after¬ 
wards  to  pass  through  the  hands  of  the  cutter  is  always  made 
of  considerable  thickness,  and  requires  not  only  that  the  heat 
ot  the  oven  should  be  very  considerable  when  it  is  first  inserted, 
but  that  it  should  be  withdrawn  from  this  heat  very  gradually  j 
while,  on  the  contrary,  such  articles  as  are  very  thin  may  be 
placed  at  first  in  a  much  more  moderate  temperature,  and  may 
be  removed  altogether  at  the  expiration  of  a  few  hours. 


CHAP.  IV.  FLINT  GLASS.  143 

It  is  impossible  by  written  explanations  to  impart  beyond  a 
very  faint  idea  of  the  truly  curious  and  interesting  operations 
of  the  glass-blower.  This  difficulty  does  not  arise  from  any 
complexity  in  the  manipulations.  Although,  in  common  with 
nearly  all  the  manual  arts,  these  call  for  long  practice  to  insure 
proficiency,  they  are  yet  exceedingly  simple  in  their  nature. 
But  there  is  something  more  than  ordinarily  striking — perhaps, 
even,  it  may  be  said  fascinating — in  watching  the  progress 
through  which  a  substance,  in  its  usual  state  rigid  and  brittle  to 
a  proverb,  passes,  by  rapid  conversion,  from  a  glowing  and 
shapeless  lump  to  a  perfect  article  of  most  elegant  manufac¬ 
ture.  The  absolute  control  which  the  workman  exercises  over 
its  form  and  substance ;  the  perfect  ease  and  security  where¬ 
with  he  pulls,  and  twirls,  and  divides,  and  joins,  a  matter  which 
we  are  accustomed  to  handle  with  only  gentleness  and  care ; 
never  fail  to  excite  a  high  degree  of  admiration  even  in  those 
who  have  had  frequent  opportunities  for  witnessing  the  pro¬ 
cesses. 

The  amusement  to  be  derived  from  watching  the  operations 
employed  in  many  branches  of  manufacture  is  probably  much 
greater  than  would  be  imagined  by  persons  who  have  not  so  in¬ 
dulged  their  curiosity ;  and  among  these  manufactures,  al¬ 
though  there  are  doubtless  many  that  call  in  a  higher  degree 
for  our  admiration  as  proofs  of  the  genius  and  perseverance  of 
man,  there  is  not  one  calculated  to  afford,  for  the  time,  more 
gratification  than  the  operations  of  a  glass-house. 


CHAP.  V. 

ON  THE  MANUFACTURE  OF  CROWN  GLASS,  BROAD  GLASS,  AND 
BOTTLE  GLASS. 

Description  of  Crown  Glass. — Harder  than  Flint  Glass. — More  difficult  to 
Fashion. — Its  Composition. — In  France. — In  England. — Fritting. — Cullet. 
—Refining. — Sulphate  of  Soda. — Vegetable  Charcoal. — Gathering. — Blow¬ 
ing.— Reheating. — Flattening. — Transferring  to  Pontil. — Twirling. — Ex¬ 
panding.— Opening. — Annealing.— Nice  Regulation  of  Temperature  re¬ 
quired  in  this  Process. — dualities  of  Crown  Glass.— German  Glass. — 
Broad  Glass. — Inferior  to  Crown  Glass. — Its  Composition. — Preparation. 
— Working. — Bursting. — Opening. — Annealing. — Bottle  Glass. — Manufac¬ 
ture  checked  by  Increase  of  Duty. — Composition. — Restrictions  as  to  Ma¬ 
terials. — Their  bad  Tendency. — Superiority  of  Bottle  Glass  for  certain 
Purposes. — Materials  employed  in  France. — At  Newcastle. — Fashioning. 
— Moulding. — Experiments  suggested  by  Count  Chaptal. — Klingstein. — 
Volcanic  Granite. 

The  name  of  crown  glass  is  given  to  the  best  kind  of  glass 
commonly  used  in  making  windows,  and  for  like  purposes.  In 
the  composition  of  this  material,  no  lead  or  metallic  oxide  en- 


144 


GLASS  MANUFACTURE. 


CHAP.  V. 


ters  as  a  fluxing  agent.  A  small  quantity  of  manganese  is  fre¬ 
quently  used,  and  sometimes  also  a  minute  portion  of  oxide  of 
cobalt ;  but  the  object  of  these  additions  is  the  correction  of  a 
faulty  color  in  the  glass,  arising  from  impurities  in  the  sand  and 
alkali.  This  kind  is,  therefore,  much  harder  than  flint  glass, 
and  would  consequently  be  more  difficult  to  fashion,  if  it  were 
desired  to  give  it  any  other  form  than  that  of  a  plane  surface. 

The  composition  of  crown  glass  varies  considerably.  Loysel 
has  given  several  different  recipes  for  its  formation.  That 
which  he  most  recommends,  stating  that  it  is  employed  at  the 
extensive  works  of  St.  Gobain,  consists  of 


Fine  white  sand . 100  parts. 

Carbonate  of  lime . 12 


Carbonate  of  soda,  calcined,  45  to  48 
Clippings  of  crown  glass  .  .  100 ; 
with  such  additions  of  manganese  and  oxide  of  cobalt,  as  may 
be  required  to  correct  impurities  and  remove  the  color  which 
they  occasion.  By  proper  carefulness  in  selecting  and  purify¬ 
ing  the  ingredients,  the  employment  of  these  metallic  bodies  is 
rendered  unnecessary. 

Crown  glass  is  generally  made  in  France  of  100  parts  of 
fine  white  sand,  50  to  65  parts  potash,  6  to  12  parts  dry  slaked 
lime  in  powder,  and  from  10  to  100  parts  of  broken  glass  of 
similar  quality  :  this  composition  is  frequently  employed  in 
that  country  for  the  manufacture  of  common  drinking  vessels, 
as  well  as  of  window  panes. 

In  England,  this  material  has  usually  been  composed  of  fine 
Lynn  sand,  kelp,  and  slaked  lime  ;  the  proportions  of  these  in¬ 
gredients  varying  according  to  the  quality  of  the  kelp,  some 
kinds  of  which  contain  a  greater  amount  of  alkali  than  others. 
That  from  Orkney  is  considered  to  be  the  best,  not  only  on  this 
account,  but  also  because  the  glass  which  is  made  of  it  proves 
of  a  better  color  than  where  Scotch  or  Irish  kelp  is  employed. 
The  proportions  when  the  kelp  is  of  the  best  quality  are, 

Fine  sand  ....  5  bushels  or  200  pounds’  weight, 


Ground  kelp  .  11 . 330 

Slaked  lime . 15 ; 


which  ingredients  are  fritted  in  the  calcar  as  already  described, 
preparatory  to  their  fusion.  When  put  into  the  crucible,  about 
half  its  weight  of  broken  glass,  or,  as  it  is  called  in  the  manu¬ 
factory,  cullet,  is  added  to  the  frit.  This  compound  requires  to 
be  kept  in  fusion  at  a  high  degree  of  heat  during  thirty-five  to 
forty  hours,  in  which  time  an  intimate  union  of  all  the  parts 
takes  place ;  the  glass  refines  itself  by  throwing  off  all  its  san- 
diver,  and  becomes  perfectly  transparent.  It  is  not  advisable  to 
use  a  larger  proportion  of  broken  and  refuse  glass  than  that 


CHAr.  V. 


CROWN  GLASS. 


145 


just  mentioned,  because,  by  its  long  exposure  to  heat  when  in 
fusion,  glass  is  made  to  give  up  a  portion  of  its  alkali,  becoming 
harsher  and  less  fusible.  The  quantity  of  glass  usually  em¬ 
ployed  is  serviceable  by  sooner  bringing  the  pot  to  a  working 
state  ;  but  any  larger  quantity  would,  for  the  reason  just  stated, 
sensibly  alter  the  quality  of  the  whole  contents  of  the  crucible. 
The  fragments,  before  they  are  used,  are  first  heated,  and  then 
suddenly  plunged  into  cold  water,  which  renders  it  easy  to  re¬ 
duce  them  to  powder. 

A  very  superior  quality  of  crown  glass  is  made  by  the  mix¬ 
ture  of 

120  parts  by  weight  of  White  sand. 


60 . Purified  pearl-ash, 

30 . Saltpetre, 

2 . Borax, 

1 . Arsenic. 


If  the  color  should  prove  yellow,  this  is  corrected  by  the  ad¬ 
dition  of  a  small  quantity  of  manganese. 

Another  composition,  cheaper  than  the  foregoing,  consists  of 
120  pounds  of  White  sand, 


50 . Unpurified  pearl-ash, 

20 . Common  salt, 

10 . Saltpetre, 

4 . Arsenic, 


and  3  ounces  of  Manganese. 

This  produces  glass  of  a  good  and  useful  description,  much  em¬ 
ployed  in  the  manufacture  of  apothecaries’  vials. 

The  late  M.  Gehlen,  who  was  well  experienced  in  the  art 
of  glass-making,  composed  crown  glass  of  the  following  ma¬ 
terials*: — 

Sand . 100  parts. 

Dry  sulphate  of  soda  .  .  50 

Quick-lime  in  powder  .  17  to  20 

Charcoal .  4. 

In  this  case  the  sulphuric  acid  in  combination  with  the  soda  is 
decomposed  by  the  charcoal,  and  driven  off  during  the  fusion, 
leaving  the  soda  to  unite  with  the  sand.  M.  Gehlen  made 
many  experiments  to  ascertain  the  effects  of  various  combina¬ 
tions  with  sulphate  of  soda,  and  found  that  this  salt  could  be 
used  without  the  addition  of  any  other  saline  flux.  If  mixed 
with  only  sand,  the  vitrification  was  very  imperfect  even  after 
long-continued  heat.  The  addition  of  lime  caused  it  to  suc¬ 
ceed  better,  but  the  time  and  fuel  required  were  still  excessive. 
When,  however,  by  the  addition  of  vegetable  charcoal,  the  sul- 


*  Annates  de  Cliimie  et  de  Physique.  Fevrier,  1816. 

N 


146 


GLASS  MANUFACTURE. 


CHAP.  V. 


phuric  acid  was  decomposed,  and  the  powerful  affinity  de¬ 
stroyed,  which  prevented  the  soda  from  acting  on  the  sand,  vit¬ 
rification  was  produced  both  perfectly  and  quickly.  If  used  in 
any  other  proportions  than  those  above  mentioned,  M.  Gehlen 
found  that  the  fusion  was  accompanied  by  disagreeable  sulphur¬ 
ous  odors,  and  by  an  extraordinary  swelling  over  of  the  mate¬ 
rials.  The  decomposition  of  the  sulphate  of  soda  may  be 
effected  with  equal  advantage,  either  during  or  before  vitrifica¬ 
tion,  according  as  the  choice  of  the  manufacturer  may  be  influ¬ 
enced  by  local  circumstances. 

When  the  materials  are  properly  fused  and  refined  by  the 
removal  of  all  the  glass  gall,  the  workman  commences  his 
blowing  operations  in  exactly  the  same  manner  as  has  already 
been  described  in  the  process  for  making  flint  glass.  By  re¬ 
peated  dippings  of  the  iron  tube  into  the  crucible,  he  gathers 
as  much  glass  upon  its  end  as  experience  teaches  him  will  suf¬ 
fice  for  the  formation  of  a  sheet  of  glass  of  the  usual  size,  and 
which  generally  weighs  from  ten  to  eleven  pounds.  This  lump 
he  allows  to  project  beyond  the  extreme  end  of  the  tube  ;  and 
first  rolling  it  on  the  iron  plane  before  described,  to  give  the 
glass  a  cylindrical  form,  he  commences  blowing,  when,  it  as¬ 
sumes  the  shape  of  a  pear.  A  fresh  heating  and  a  second  blow¬ 
ing  enlarge  its  dimensions,  and  render  its  shape  more  globular. 
A  third  operation  of  heating  and  blowing  still  further  enlarges 
the  size  of  the  glass,  and  reduces  its  substance.  The  side  op¬ 
posite  to  the  tube  is  then  flattened  by  pressure  against  a  plane 


Fig.  10. 


surface  ;  a  small  portion  of  melted  glass  is  collected  on  the  end 
of  a  punt,  and  is  applied  to  the  centre  of  this  flattened  side, 
forming  an  union  with  it  exactly  opposite  to  the  hollow  tube, 


CHAP.  V.  CROWN  GLASS.  -  147 

which  is  then  removed  by  wetting  the  glass  near  to  their  point 
of  union,  leaving  a  circular  hole  in  the  glass  about  two  inches 
in  diameter. 

At  this  period  the  glass  must  be  again  held  to  one  of  the 
openings  ot  the  furnace  until  it  has  become  sufficiently  hot  and 
ductile  for  the  further  alteration  of  its  shape.  The  workman 
then  dexterously  twirls  the  punt  in  his  hand,  slowly  at  first, 
and  then  more  and  more  quickly,  when  the  glass  yields  to  the 
centrifugal  impulse ;  its  diameter  becomes  greater  and  greater ; 
the  hole  just  mentioned  expands  proportionally ;  and  when  in 
this  continued  progression  the  doubled  portion  opposite  to  the 
iron  rod,  and  between  the  periphery  of  the  glass  and  the  ori¬ 
fice,  is  diminished  to  an  annulus  or  ring  only  a  few  inches 
wide,  this  in  an  unaccountable  manner  instantly  flies  com¬ 
pletely  open,  and  the  glass  is  converted  into  a  plane  disc  of 
fifty  to  sixty  inches  diameter,  having  an  uniform  thickness 
throughout  the  entire  plate,  with  the  exception  of  the  spot 
where  it  is  attached  to  the  iron  rod,  and  where  there  is  a  knot 

Fig.  11. 


or  lump  which  is  called  a  bull's  eye.  Twelve  of  these  plates 
make  up  what  is  called  a  crate  or  side  of  glass. 

The  effect  of  this  operation  upon  persons  who  witness  it  for 
the  first  time  is  both  pleasing  and  surprising  in  a  high  degree. 
The  force  wherewith  the  glass  flies  open  at  the  close  of  the 
process  would  be  sufficient,  if  its  brittleness  were  not  removed 
by  heat,  to  break  it  into  innumerable  fragments. 

The  plate,  when  thus  finished,  is  detached  from  the  iron  rod 
by  the  usual  method,  and  placed  resting  on  its  edge  in  the  an- 


148 


GLASS  MANUFACTURE. 


CHAP.  V. 


nealing  oven.  Some  considerable  care  is  necessary  for  regula¬ 
ting  the  temperature  at  this  stage ;  for  if  the  heat  be  too  great, 
the  softened  glass  will  bend,  and  for  that  reason  will  be  lessen¬ 
ed  in  value,  while,  if  the  oven  be  not  sufficiently  hot,  the  plates 
are  very  likely  to  crack ;  and  if  even  this  disaster  should  not 
happen,  the  glass  will  prove  of  inferior  quality,  and  so  brittle, 
that  the  glazier  will  be  unable  to  cut  it  with  any  degree  of  cer¬ 
tainty  in  the  wished-for  direction. 

Crown  glass  is  sold,  according  to  its  quality,  under  four  dif¬ 
ferent  denominations — firsts,  seconds,  thirds,  and  fourths — at 
considerable  difference  of  price ;  that  of  the  fourth  quality  not 
yielding  to  the  manufacturer  nearly  one  half  of  the  price  of 
the  first.  These  variations  arise  principally  from  the  want  of 
sufficient  care  on  the  part  of  the  attendants,  in  maintaining  the 
necessary  degree  of  heat  in  the  furnace.  If  this  is  once  suffer¬ 
ed  to  fall,  the  property  of  glass  in  being  a  very  imperfect  con¬ 
ductor  of  heat  renders  it  difficult  again  to  raise  it  to  the  former 
degree.  In  the  operations  of  a  large  glass-house,  it  does  not 
often  happen  that  beyond  one  third  of  the  quantity  made  is  of 
the  first  quality ;  seconds  and  thirds  compose  the  largest  propor¬ 
tion  of  the  produce;  and  it  seldom  occurs  that  the  quality 
sinks  below  the  latter  of  these  two  denominations. 

Large  plates  ofcrown  glass,  such  as  are  required  for  glazing 
engraved  prints,  used  formerly  to  be  imported  from  Germany. 
This  country  has,  however,  for  a  long  time,  been  not  only  in¬ 
dependent  in  this  respect  of  all  foreign  manufacturers,  but 
similar  plates  of  English  make  are  exported  to  a  considerable 
extent. 

Broad  glass  is  a  common  coarse  description  of  window  glass, 
made  of  inferior  ingredients,  and  by  a  somewhat  different  pro¬ 
cess  of  manufacture  than  that  last  described.  The  material 
principally  employed  for  the  purpose  is  soap-boiler’s  waste. 
This  compound  is  a  pasty  mass,  consisting  of  the  insoluble  mat¬ 
ter  of  the  kelp  or  barilla,  and  of  the  lime  which  has  been  used 
to  render  the  alkali  caustic,  together  with  a  quantity  of  salt 
and  water.  This  substance  is  united  with  kelp  and  sand,  and 
the  mixture  is  dried  and  fritted.  The  proportions  wherein  the 
ingredients  are  used  necessarily  vary  according  to  the  quality 
of  the  principal  constituents,  and  the  manufacturer  must  be 
guided  by  practical  knowledge  in  apportioning  the  quantities. 

A  very  usual  mixture  is  six  measures  of  soap-boiler’s  waste, 
three  of  kelp,  and  three  to  four  measures  of  sand.  The  quality 
of  the  last  of  these  ingredients  is  of  greater  moment  to  the 
manufacturer  than  would  seem  to  be  generally  imagined. 
Coarse  sand  is  known  to  require  a  greater  quantity  of  alkali 
for  its  fusion  than  that  which  is  fine;  and  as,  notwithstanding 


CHAP.  V. 


BROAD  GLASS. 


149 


this,  the  glass  when  made  does  not  contain  the  alkali  m  a 
larger  proportion,  it  follows,  that  the  difference  has  been  dissi¬ 
pated  and  lost  during  the  process.  The  carbonaceous  matter, 
which  would  injure  the  color  of  the  glass,  is  principally  burned 
out,  and  the  carbonic  acid  gas  separated  during  the  fritting; 
after  the  completion  of  which,  the  mass,  still  red-hot,  is  re¬ 
moved  with  iron  shovels  to  the  melting  furnace,  the  crucibles 
are  entirely  filled,  and  after  twelve  or  sixteen  hours’  exposure 
to  the  proper  degree  of  heat,  the  whole  is  perfectly  vitrified. 

The  formation  of  this  glass  into  sheets  is  thus  performed : — 
The  necessary  quantity  being  collected  upon  the  end  of  the 
iron  tube,  as  already  described,  is  expanded  by  the  workman’s 
breath  into  a  globular,  or  rather  into  an  elliptical  shape,  of  about 
twelve  inches  diameter,  and  of  the  requisite  thickness.  This 
done,  the  glass  is  carried  to  the  mouth  of  the  oven ;  and  the  end 
of  the  tube  through  which  the  workman  has  blown  being 
closed,  the  further  expansion  by  heat  of  the  confined  air  causes 
the  glass  to  burst  in  its  weakest  part.  While  still  hot  and  duc¬ 
tile,  it  is  then  opened  by  a  pair  of  shears  through  its  entire 
length  into  a  flat  plate,  which  is  then  conveyed  to  the  anneal¬ 
ing  oven. 

More  than  one  half  of  the  entire  manufacture  of  glass  in 
Great  Britain  is  composed  of  common  green  bottle  glass.  The 
quantity  of  this  material  upon  which  duty  has  been  levied,  on 
an  average  of  the  last  six  years,  exceeds  11,000  tons  annually. 
However  considerable  this  amount  may  appear,  it  is  not  greater 
than  the  annual  average  manufacture  of  a  similar  period  com¬ 
mencing  in  the  year  1790, — a  fact  which  may  be  thought  ex¬ 
traordinary,  when  it  is  considered  that  during  the  intervening 
years  our  population  has  been  importantly  augmented  ;  that  the 
comforts,  and  even  the  luxuries  of  life,  have  been  brought  with¬ 
in  the  reach  of  a  much  larger  proportion  of  our  fellow-country¬ 
men  ;  and  that  our  colonial  markets  have,  in  the  same  time, 
been  very  considerably  extended.  The  circumstance  of  the 
rate  of  duty  having  been  doubled  would  hardly  appear  cause 
sufficient  for  thus  arresting  the  progress  of  consumption  in  an 
article  so  generally  required;  since  this  duty,  at  its  highest 
rate,  has  never  exceeded  eight  shillings  per  himdred  weight. 
A  more  minute  examination  into  the  case  leaves  us,  however, 
without  any  reason  for  doubting  that  to  the  increase  of  the 
rate  of  duty,  and  to  it  alone,  is  to  be  ascribed  the  check  given 
to  this  branch  of  manufacture.  In  the  year  1812,  when  the 
duty  was  4s.  0-ty.  per  hundred  weight,  upwards  of  13,000  tons 
of  common  bottle  glass  contributed  towards  the  revenue.  In 
the  succeeding  year,  when  an  additional  tax  of  4s.  0 §<Z.  was 
imposed,  the  consumption  immediately  fell  to  somewhere  below 

N  2 


150 


GLASS  MANUFACTURE. 


CHAP.  V. 


8000  tons.  From  this  extreme  depression  it  has  since  gradu¬ 
ally  risen,  through  the  increasing  numbers  and  improved  con¬ 
dition  of  the  community,  and  aided  by  a  diminution  of  price, 
independent  of  the  duty ;  but  even  now  the  manufacture  has 
not  reached  within  2500  tons  of  the  point  which  it  had  attain¬ 
ed  in  the  year  1812;  thus  in  a  very  striking  manner  verifying 
the  remark  so  often  made  as  to  the  variance  between  common 
and  legislative  arithmetic,  and  proving  the  pernicious  tendency 
of  taxes  levied  upon  articles  of  domestic  manufacture.  It  is  to 
be  hoped  that  the  improvement  of  the  national  revenue  conse¬ 
quent  upon  the  progressive  state  of  our  manufacturing  inte¬ 
rests,  and  the  constantly  ameliorating  circumstances  of  many 
classes  of  the  community,  will  enable  the  government  to  carry 
speedily  into  effect  a  measure  already  announced  for  abolishing 
entirely  the  duties  upon  glass  of  home  fabric,  when  this  branch 
of  the  manufacture  will  assuredly  receive  an  impulse  that  will 
carry  it  far  beyond  the  highest  point  to  which  it  has  ever  yet 
attained. 

The  composition  of  bottle  glass  is  as  little  uniform  as  that  of 
any  other  description  of  the  material ;  varying  greatly  in  differ¬ 
ent  parts  of  the  kingdom,  and  indeed  in  almost  every  individ¬ 
ual  manufactory.  It  is  usually  made  of  sand,  lime,  and  some¬ 
times  clay,  any  kind  of  alkali  or  alkaline  ashes  which  may  hap¬ 
pen  to  offer  the  greatest  inducement  in  point  of  price,  and  some¬ 
times  the  vitreous  slag  produced  from  the  fusion  of  iron  ore. 
Soap-makers’  waste  is  frequently  used  in  the  proportion  of  three 
measures  to  one  measure  of  sand. 

The  rate  of  duty  upon  this  description  of  glass  being  only 
one  eighth  of  that  levied  upon  flint  glass,  the  manufacturers 
are  restricted  to  the  use  of  the  commonest  kind  of  sea  or  river 
sand,  lest  the  revenue  should  suffer  by  the  superior  quality  of 
this  less  burdened  ware.  This  is  unfortunate,  since,  for  the 
reason  already  given,  the  employment  of  such  coarse  sand  oc¬ 
casions  the  necessity  for  using  a  large  portion  of  alkaline  mat¬ 
ter,  and,  in  that  respect,  increases  the  charges  to  the  glass- 
blower.  The  impurity  of  the  alkali,  and  the  abundance  of  flux¬ 
ing  materials  of  an  earthy  nature,  joined  to  the  very  high  degree 
of  heat  at  which  they  are  fused,  occasion  the  glass  to  contain  a 
very  small  proportion  of  real  saline  matter ;  for  which  reason  it 
is  better  qualified  than  flint  glass  to  be  employed  as  the  recipi¬ 
ent  of  fluids  which  have  any  corrosive  action.  Chemical  re¬ 
torts  and  subliming  vessels,  and  carboys  for  containing  aqua¬ 
fortis,  should,  for  this  reason,  be  always  made  with  this  common 
glass,  which  has  this  further  advantage  over  flint  glass — that  it 
will  bear  a  much  stronger  heat  without  being  softened  or  un¬ 
dergoing  any  alteration  of  its  shape. 


CHAP.  V. 


BOTTLE  GLASS. 


151 


.  ®?,ttIe  £las.3  13  a  very  hard  and  well  vitrified  substance,  and 
is  of  less  specific  gravity  than  other  descriptions.  Loysel  erives 
as  the  composition  usually  employed  in  France  for  the  produc¬ 
tion  of  this  material, —  ^ 

Common  white  or  yellow  sand  .  .  100  parts. 

Coarse  kelp .  30  to  40 

Lixiviated  earth  of  ashes . 160  to  170 

Fresh  wood  or  other  ashes  ....  30  to  40 
Yellow  clay,  or  brick  earth  ...  80  to  100 
Broken  glass  ad  libitum,  usually  100 ; 
which  composition  does  not  produce  any  glass  gall. 

At  Newcastle  upon  Tyne,  where  the  manufacture  of  bottle 
glass  is  much  encouraged  by  the  excessive  cheapness  of  small 
coal,  or  slack,  the  manufacturers  employ  a  mixture  of  lime  and 
feea  sand.  This  must  be  frequently  wetted  with  sea  water, 
which,  on  evaporating,  deposits  its  salt;  the  soda  contained  in 
this  being  the  only  alkali  employed.  When  combined  with 
silica,  and  exposed  to  a  high  degree  of  heat,  lime  appears  to  be 
endued  vvitii  the  property  of  decomposing  common  salt;  its 
presence  is,  therefore,  essential  to  the  success  of  this  operation. 

Articles  made  of  bottle  glass  are  fashioned  by  the  same  pro¬ 
cess  as  those  of  flint  glass,  with  the  exception  of  wine  and  beer 
Dottles,  the  containing  parts  of  which  are  blown  in  metallic 
moulds,  m  order  to  keep  them  nearly  of  an  uniform  size.  The 
?reen  color  of  this  glass  is  owing  to  the  presence  of  a  portion 
31  iron  in  the  sea  sand,  and,  probably  also,  in  the  vegetable  ashes 
3f  which  it  is  composed. 

I fj* during  the  time  when  the  workmen  are  employed  in 
moulding  and  blowing  bottles,  the  melted  glass  should— as  bl¬ 
eed  it  frequently  will — become  cooler  than  is  desirable  for  the 
lurpose,  so  that  it  is  found  necessary  to  replenish  the  fire,  so 
much  dust  will  be  thus  occasioned,  owing  to  the  description  of 
:oal  employed,  that  the  surface  of  the  melted  glass  will  be  cov¬ 
ered  with  carbonaceous  matter.  The  effect  of  this  upon  the 
contents  of  the  crucible  is  very  curious.  The  glass,  which  had 
ietore  remained  perfectly  quiet,  becomes  suddenly  so  disturbed 
nroughout  as  to  present  the  appearance  of  violent  ebullition, 
nd  the  whole  mass  is  immediately  crowded  with  an  infinite 
mmber  of  minute  air-bubbles,  which,  so  long  as  they  are  suffer- 
d  to  remain,  render  the  glass  wholly  unfit  for  use. 

he  time  that  would  be  required  for  burning  away  this  car- 
onaceous  deposit,  and  to  restore  the  glass  to  its  former  working 
rate,  would  be  so  considerable,  that  it  would  be  highly  incon- 
ement  to  wait  for  the  production  of  this  effect ;  and  it  is  there- 
)re  fortunate  that  a  simple  remedy  has  been  discovered,  which 


GLASS  MANUFACTURE. 


CHAP.  V. 


152 

immediately  and  perfectly  restores  every  thing  to  its  former 
state. 

Whenever  the  accident  here  mentioned  occurs,  the  work¬ 
man  has  only  to  throw  a  small  quantity  of  water  into  the  cruci¬ 
ble,  when  the  whole  mass  will  be  immediately  stilled,  and  the 
bubbles  will  as  instantly  disappear,  so  that  the  workman  may 
proceed  without  further  delay.  This  curious  effect  has  been 
referred  to  the  decomposition  by  heat  of  the  water,  which,  giv¬ 
ing  up  its  oxygen  to  the  coal-dust,  converts  it  into  carbonic  acid 
gas ;  in  which  form  it  is  instantly  driven  off  by  the  excessive 
heat  of  the  furnace,  and  is  dissipated  in  the  atmosphere. 

In  1780,  the  celebrated  M.  Chaptal  recommended  M.  Ducros, 
a  manufacturer  of  bottle  glass,  to  make  trial  of  a  new  material 
for  his  purpose.  This  gentleman  entered  in  consequence  upon 
various  experiments,  which  were,  many  of  them,  to  a  certain 
extent,  successful.  The  substance  thus  recommended,  and 
which  formed  the  basis  of  these  experiments,  was  decomposed, 
pulverulent,  basaltic  earth.  This  is  found  in  great  abundance 
in  many  parts  of  France,  and  is  equally  obtainable  in  the  valleys 
of  all  basaltic  countries. 

In  the  first  trial  made  of  this  earth  by  M.  Ducros,  it  was  fused 
in  a  glass  pot  without  admixture  with  any  other  substance ;  and 
the  result  obtained  was  glass  of  an  exceedingly  deep  yellow 
color,  and  lustrous.  In  subsequent  experiments,  various  pro¬ 
portions  of  sand  were  used  in  conjunction  with  the  basaltic 
earth.  The  mixture  that  was  found  to  answer  the  purpose  best 
was  where  equal  parts  of  each  ingredient  were  employed.  This 
produced  glass  of  an  olive  green  color.  .• 

There  was  tor  some  time  a  considerable  demand  for  bottles 
thus  composed ;  but  owing  to  a  difficulty  which  the  manufac¬ 
turer  experienced  in  procuring  materials  having  the  requisite 
uniformity  in  their  constituent  parts,  the  manufacture  was,  after 
a  time,  abandoned. 

M.  Alliot  has  published  the  results  of  a  course  of  experiments 
made  by  him  with  basaltic  earth,  with  a  view  to  the  composi¬ 
tion  of  glass.  Not  being  able  to  have  recourse  to  the  furnace 
of  a  glass-house,  M.  Alliot  was  obliged  to  content  himself  with 
the  less  intense  heat  of  a  potter’s  kiln,  wherein  the  different 
mixtures  which  he  employed  were  severally  heated  during 
eighteen  hours.  It  is  probable  that  the  results  which  he  has 
detailed  would  have  proved  more  satisfactory,  could  recourse 
have  been  had  to  a  more  efficient  mode  of  heating.  The  ex¬ 
periments  were  all  conducted  in  crucibles. 

No.  1.  was  filled  with  the  pure  basaltic  earth.  This,  in  fusing, 
was  converted  into  a  black  glass,  which  was  opaque,  and  tol¬ 
erably  well  melted. 


HAP.  V.  BOTTLE  GLASS.  153 

o.  2.  contained  a  mixture  composed  in  equal  parts  of  basalt, 
ashes,  and  white  quartz  in  powder.  This  produced  a  coffee- 
colored  glass,  which  was  lustrous,  and  somewhat  resembled 
porcelain  in  appearance. 

o.  3.  was  charged  with  half  basalt  and  half  common  sand. 
The  glass  produced  from  this  compound  appeared,  when  in 
the  mass,  of  a  blue-black  color;  but  when  small  thin  portions 
were  examined,  these  proved  of  a  yellowish  green.  This 
glass  was  tolerably  well  melted. 

o.  4.  consisted  of  one  third  each  basaltic  earth,  sand,  and  re¬ 
fuse  soda.  The  result  was  a  transparent  glass  of  a  greenish 
yellow  color,  and  of  good  quality  ;  it  was  very  smooth  and 
shining,  well  melted,  and  would  have  formed  excellent  bot¬ 
tles. 

).  5.  consisted  wholly  of  sand  taken  from  the  river  Orb,  in 
the  immediate  neighborhood  of  which  there  is  found  a  con¬ 
siderable  quantity  of  basaltic  earth.  The  glass  from  this  sand 
was  well  melted,  and  appeared  to  be  every  way  adapted  for 
the  manufacture  of  very  good  and  serviceable  glass  bottles. 

This  basaltic  earth  is  exceedingly  well  qualified  both  for  fU- 
n  by  itself,  and  for  employment  as  a  fluxing  material  where 
ier  substances  are  used.  It  is  found,  by  analysis,  to  contain 
)ut  45  parts  of  silex,  16  of  alumine,  20  of  oxide  of  iron,  9  of 
ie,  and  from  2%  to  4  parts  of  pure  soda ;  three  of  these  sub- 
nces  being  very  powerful  fluxes. 

Some  other  minerals  have  been  proposed,  on  account  of  the 
a  which  they  contain,  as  well  qualified  for  making  glass : 
;h,  for  instance,  is  klingstein,  which  contains  nearly  one 
slflh  part  of  its  weight  of  that  alkali ;  but  as  the  other  flux- 
'  materials  present  in  basaltic  earth  are  wanting  in  those 
er  minerals,  they  prove  far  less  fusible. 

Whenever  basaltic  earth  is  largely  employed  in  the  compo- 
on  of  glass,  it  usually  proves  of  a  dark  olive  green  color, 
ying  sometimes  to  a  very  deep  yellow7 ;  and  it  does  not  ap- 
r  at  all  probable  that  this  color  could  in  any  material  degree 
corrected.  The  glass  produced  is  specifically  lighter  than 
common  green  bottle  glass ;  and  at  the  same  time  is  con- 
;rably  harder  and  tougher,  so  as  to  bear,  without  injury, 
vs  which  would  infallibly  break  ordinary  glass.  The  quan- 
of  alkali  which  it  contains  is  small — much  smaller,  in  fact, 
i  is  required  to  bring  glass  of  every  other  description  to  a 
kable  state.  For  this  reason  basaltic  glass  is  peculiarly  well 
iified  for  chemical  purposes ;  as  vessels  made  with  it  will 
3t  the  destructive  action  of  corrosive  liquids. 
i  addition  to  the  experiments  already  detailed  as  having 


154  GLASS  MANUFACTURE.  CHAP.  V 

been  made  by  him  with  basaltic  earth,  M.  Alliot  made  trial  c 
various  other  combinations  for  the  production  of  bottle  glas 
He  succeeded  with  the  two  following  : 

The  first  was  a  mixture  in  equal  parts  of  ashes  and  a  vole 
nic  granite.  This  fused  perfectly,  and  produced  a  very  fii 
dark  and  lustrous  glass,  exceedingly  well  qualified  for  the  cor 
position  of  bottles.  The  second  was  composed  of  1  part  ore 
nary  soda,  12  parts  ashes,  and  6  parts  common  sand.  The  gla 
thus  formed  was  of  a  yellowish  black  color,  interspersed  wi 
veins  of  bluish  white,  which  were  opaque. 

When  the  duty  shall  be  removed,  and  the  manufacturer  fin 
himself  without  restriction  in  regard  to  the  materials  which  i 
may  employ,  we  may  expect  to  witness  some  considerable  ii 
provements  in  this  branch  of  the  glass-maker  s  art. 


CHAP.  VI. 


OF  THE  MANUFACTURE  OF  PLATE  GLASS. 


Different  Descriptions  of  Plate  Glass.-Blown  Plates  limited  in  Size -C 
Plate  Works  at  Ravenhead. — Difficulties  of  the  Process.— Materials, 
nous  Compositions.-  Borax.-  Mixing  Mahals. -^tting.-Furaa 
ami  Crucibles  at  St.  Gobain.— Pots.—Cuvettes.--Regulation  of  Firin^. 
Castin"  Tables. — Arrangement  of  Foundery  at  Ravenhead.  Anneal 
Ovens -Process  of  Casting  Plates.— Annealing.— Squaring.— Gnndine 
Economical  Improvement.— Smoothing.— Emery  Powder.— Comparat 
Value  of  Large  and  Small  Plates.— Polishing.— Si  vering.— Preparation 
Amalgam. — Mode  of  its  Application.— Blowing  Plate  Glass.— Punching 
Partial  Cutting.— Transfer  to  Pontil. — Completion  of  Cutting.— Openi 
—Sizes  of  Plates.— Effect  of  Sun’s  Rays  in  Discoloring  Plate  Glass. 


Two  descriptions  of  plate  glass  are  made :  one  by  blowi 
and  opening,  in  the  manner  of  broad  glass,  as  already  describe 
the  other  by  casting  the  melted  materials  upon  a  plane  meto. 
surface,  somewhat  in  the  manner  pursued  for  makmg  sh 

leapiates  of  glass  which  are  blown  are  necessarily  limited 
their  size,  although  some  of  considerable  dimensions  are  p 
duced  in  this  way.  When  cast,  the  extent  of  the  plates  n 
be  much  greater ;  and,  indeed,  is  limited  only  by  the  very  he; 
expense  attending  the  erection  of  machinery,  and  the  prose 
tion  of  the  manufacture  in  its  various  parts.  Different  ma 
factories  have  been  established  at  various  times  in  this  krngt 
for  the  production  of  plate  glass  by  blowing,  but  these,  one  at 
another,  have  mostly  been  discontinued.  The  last  estabh 
ment  of  this  kind  in  London  existed  a  very  few  years  since 
East  Smithfield ;  but  being  a  private  establishment,  and 
proprietors  finding  it  impossible  to  continue  a  successful  com 


HAI*.  VI. 


PLATE  GLASS.  155 

ition  with  the  powerful  corporate  body  alluded  to  in  the  first 
hapter  of  this  treatise,  the  works  have  been  discontinued  ;  and 
tie  only  place  in  England  where  plate  glass  of  any  great  mag¬ 
nitude  is  now  manufactured,  is  on  the  premises  of  the  British 
ate  Glass  Company  in  Ravenhead,  in  Lancashire,  where 
lates  are  cast  which  equal,  in  every  respect,  the  produce  of 
1  e  French  manufactory  at  St.  Gobain.  The  office  of  this  cor- 
oration  is  at  the  foot  of  Blackfriars  Bridge,  in  London ;  and 
ere  plates  of  glass  of  the  most  perfect  quality,  and  of  all  di- 
lensions  up  to  the  prodigious  length  of  160  inches,  may  at  all 
mes  be  procured. 

j  Great  reluctance  has  always  been  evinced  by  the  proprietors 
j;  P  ‘lte  glass  works  to  permit  their  examination  by  visitors, 
ersons  are,  indeed,  occasionally  admitted  to  view  the  myste- 
es;  but,  either  by  their  habits  and  rank  in  life,  such  individ- 
ils  are  unqualified  or  unlikely  to  describe  what  they  witness: 
■’ tJie  rejaxation  is  made  in  their  favor  under  a  seal  of  confi- 
P“ce,  which  renders  it  impossible  that  they  should  impart  the 
formation  they  have  acquired.  The  late  Mr.  Parkes  appears 
1  have  been  fortunate  in  this  respect;  and  having  obtained 
emission  to  visit  the  works  at  Ravenhead,  was  not  restrained 
om  publishing  a  short,  but  interesting,  account  of  the  pro- 
Pses  which  he  witnessed.  From  this  source  the  following 
ascription  is  drawn,  as  far,  at  least,  as  relates  to  the  buildings 
id  arrangements  particularly  used  at  Ravenhead. 

IMore  care  in  the  choice  of  materials,  and  greater  nicety  in 
inducting  the  processes,  are  required  for  the  preparation  of 
ate  glass  than  are  needed  in  any  other  branch  of  the  manu- 
oture.  ihe  materials  employed  are  sand,  soda,  and  lime,  to 
bich  are  added  manganese  and  oxide  of  cobalt  as  decoloring 
bsiances.  The  sand  must  be  of  the  finest  and  whitest  kind  : 
e  grains  should  be  sharp,  and  of  a  moderate  size ;  if  very 
lall,  they  are  likely  to  clot  together,  and  consequently  will 
t  mix  intimately  with  the  alkali;  and  if  the  grains  are  large, 
3y  are  on  thls  account  longer  in  being  fused.  The  sand 
ist  be  passed  through  a  wire  sieve  of  the  proper  closeness 
o  water,  and  should  be  well  agitated  to  separate  all  dirt  and 
purities.  The  alkali  used  is  always  soda :  this  is  preferred 
potash :  as  glass  made  with  the  former  substance  is  thinner, 

1  flows  better  while  hot,  and  yet  is  equally  durable  when 
a.  Ihe  quality  of  flowing  freely  is  of  the  very  first  import- 
:e  m  casting  large  plates,  which,  to  be  perfect,  require  to  be 
-bout  streak  or  bubble.  Another  advantage  attending  the  use 
s  a.  is  this ,  that  the  neutral  salts  of  which  it  is  the  base, 
b  as  muriate  and  sulphate  of  soda,  and  which,  in  this  in- 
ice,  constitute  the  glass  gall,  are  dissipated  more  readily  by 


GLASS  MANUFACTURE. 


CHAP.  VI. 


156 


the  heat  of  the  furnace,  than  are  the  salts  of  which  potash  is 
the  base.  The  soda  must  be  used  in  a  state  of  considerable  pu¬ 
rity  ;  and  is  generally  either  that  which  is  separated  from  the 
ashes  of  barilla,  and  other  soda  plants,  by  lixiviation,  or  is  pro¬ 
duced  by  the  decomposition  of  common  salt. 

Lime  acts  in  promoting  the  fusibility  of  the  silex  and  alkali, 
fulfilling  thus  the  same  office  as  is  performed  by  litharge  in  the 
manufacture  of  flint  glass.  From  one  fifteenth  to  one  twenty- 
fourth  part  of  the  whole  materials  is  the  largest  proportion  thal 
can  properly  be  used  of  lime ;  any  greater  quantity  would  im¬ 
pair  both  the  color  and  solidity  of  the  glass. 

Manganese  would  have  the  effect  of  giving  a  slight  tinge  of 
red ;  but  when  mixed  in  a  proper  proportion  with  the  blue  of 
the  cobalt,  and  both  together  are  met  by  the  natural  slight  yel¬ 
low  of  the  other  materials,  each  neutralizes  the  other,  so  tha 
scarcely  any  definable  tint  remains. 

In  addition  to  these  ingredients,  a  considerable  quantity  of 
fragments  of  glass,  or,  as  it  is  called,  cullet,  is  used  in  combina 
tion  with  the  fresh  materials.  Of  these  fragments  there  is  al 
ways  an  abundant  supply  in  the  glass-house,  produced  fron 
what  is  spilt  in  casting,  and  from  the  ends  and  edges  that  ar- 
cut  off  in  shaping  the  plates.  This  broken  glass,  or  cullet,  i 
previously  made  friable,  by  throwing  it,  while  hot,  into  col 

water.  . 

It  is  considered  that  the  addition  of  one  pound  of  pure  soda  i 
sufficient  for  four  pounds  of  sand.  But  it  is  not  enough,  in  th< 
preparation  of  glass  for  casting,  to  apply  the  alkali  only  in  th< 
proportion  necessary  to  produce  good  glass ;  much  more  thai 
this  must  be  used,  in  order  to  procure  the  requisite  degree  o: 
fluidity. 

The  composition  given  by  Loysel  as  being  used  in  the  grea 
works  at  St.  Gobain  is  this : — 


White  sand, . 160  parts 

Carbonate  of  lime,  .  12 

Soda, . . .  45  to  48 

Fragments  of  glass  of  like  quality,  ....  100 

Oxide  of  manganese, .  0£ 

Parkes  recommends  the  following  proportions,  as  qualified  t- 
produce  plates  of  glass  of  the  best  description : — 

Lynn  sand,  previously  well  washed  and  dried,  .  .  720  parts 
Alkaline  salt,  containing  40  per  cent,  of  soda,  .  .  450 


Lime,  slaked  and  sifted, .  80 

Nitre, .  25 

Cullet,  or  broken  plate  glass,  . 425 


1700 


HAP.  VI.  PLATE  GLASS.  157 

^hese  quantities  are  required  to  produce  one  pot  of  metal ,  which 
»rill  yield  1200  pounds  of  good  plate  glass. 

Another  author  states  the  following  proportions  as  being 
Hind  to  produce  very  fine  glass : — 


Fine  white  sand, .  300  pounds 

Soda, . 200 

Lime,  .  . .  30 

Oxide  of  manganese,  ......  32  ounces 

Oxide  of  cobalt, .  3 

Fragments  of  glass, .  300  pounds 


The  well-known  property  of  borax,  as  a  powerful  flux,  has 
ccasioned  the  suggestion  that,  by  its  means,  glass  made  with 
otash  might  be  caused  to  flow  in  fusion  as  freely  as  that  where- 
l  soda  is  employed.  It  has  been  asserted  that  small  quantities 
f  borax  have  always  been  used  in  the  works  at  St.  Gobain ; 
ut  the  secrecy  observed  in  regard  to  all  the  operations  canned 
n  in  that  establishment  renders  it  impossible  to  say  what  de- 
ree  of  truth  there  is  in  the  assertion. 

Great  care  is  required  in  mixing  the  materials;  much  more, 
ideed,  than  is  called  for  in  regard  to  other  kinds  of  glass.  The 
ind,  lime,  soda,  and  manganese,  being  properly  intermingled, 
re  fritted  in  small  furnaces,  wherein  the  temperature  is  grad- 
ally  raised  to  a  full  red,  or  even  to  a  white,  heat,  at  which 
oint  it  is  maintained,  and  the  materials  are  carefully  stirred 
ntil  vapor  is  no  longer  given  off,  and  no  further  change  is  un- 
ergone  by  the  materials.  This  process  of  fritting  lasts  about 
x  hours ;  and  when  it  is  nearly  completed,  the  remaining  part 
f  the  ingredients,  consisting  of  the  cobalt  and  broken  glass,  are 
Ided.  The  latter,  having  already  been  perfectly  vitrified,  does 
ot,  consequently,  require  any  lengthened  exposure  to  the  fire. 

The  furnaces  at  St.  Gobain,  in  which  the  perfect  fusion  and 
itrification  are  accomplished,  are  eighteen  feet  long  and  fifteen 
ride.  They  contain  two  kinds  of  crucibles.  The  larger  ones, 
herein  the  glass  is  melted,  are  called  pots,  and  are  formed 
ke  inverted  truncated  cones ;  the  other  crucibles,  which  are 
nailer,  are  called  cuvettes :  these  last  are  kept  empty  in  the 
irnaces,  exposed  to  the  frill  degree  of  its  heat,  that  when  the 
lass  is  ready  for  casting,  and  is  transferred  to  them,  they  may 
it  injuriously  lower  its  temperature.  The  comparative  size 
’  these  cuvettes  varies  according  to  the  dimensions  of  the 
:ates  which  it  is  intended  to  cast :  when  these  are  very  large, 
le  cuvette  will  contain  one  third  of  the  charge  of  the  pot ;  but 
i  other  cases  its  capacity  is  not  greater  than  a  fourth,  a  fifth, 

’  a  sixth  part,  of  the  contents  of  the  crucible. 

The  method  used  for  regulating  the  supply  of  fuel  to  the  fur- 

O 


158 


GLASS  MANUFACTURE. 


CHAP.  VI. 


nace  in  the  great  works  of  St.  Gobain,  is  at  once  so  rude  and 
so  absurd,  that  one  would  hesitate  to  believe  in  the  correctness 
of  the  narration,  if  it  did  not  rest  upon  good  authority.  It  is 
said  tiiat  two  persons  are  employed,  who,  being  disencumbered 
of  all  superfluous  clothing,  incessantly  run  round  the  furnace 
with  a  speed  “  equal  to  seven  leagues  in  six  hours.”  These 
men  on  their  circuit  take  up  each  two  small  billets  of  wood,  cut 
to  a  certain  size,  and  heaped  together ;  these  they  deposit  as 
they  run,  first  one  and  then  the  other,  in  the  openings  of  the 
furnace,  which  by  such  means  is  fed  at  regularly  recurring  in¬ 
tervals  of  time.  Having  continued  this  intellectual  employ¬ 
ment,  without  ceasing,  during  six  hours,  the  men  then  surren¬ 
der  their  “  seven  league  boots”  to  others,  whose  heels  and  hands 
are  similarly  employed  during  an  equal  period  of  time;  after 
which  they  are  in  turn  relieved  by  the  first  set  of  couriers. 

From  the  time  of  filling  the  pots,  it  requires  nearly  forty 
hours’  exposure  to  strong  heat,  ere  the  materials  are  properly 
vitrified  and  in  a  state  fit  for  casting.  The  processes  of  filling 
the  pots,  and  of  removing  the  glass  gall,  and  the  various  ap¬ 
pearances  that  ensue  in  the  refining,  are  precisely  similar  to 
what  has  already  been  described  in  a  former  chapter. 

When  the  glass  is  thoroughly  refined,  the  cuvette — which 
must  be  perfectly  clean,  and,  as  already  mentioned,  of  a  tem¬ 
perature  equal  with  that  of  the  glass — is  filled  in  the  following 
manner:  A  copper  ladle,  ten  to  twelve  inches  in  diameter, 
fixed  to  an  iron  handle  seven  feet  long,  is  plunged  into  the  glass 
pot,  and  brought  up  filled  with  metal  glass,  which  is  transfer¬ 
red  to  the  cuvette ;  the  ladle,  during  this  transference,  is 
supported  upon  a  strong  iron  rest,  placed  under  its  bottom, 
and  held  by  two  other  workmen.  This  precaution  is  neces¬ 
sary  to  prevent  the  bending  and  giving  way  of  the  red-hot 
copper  under  the  weight  of  fluid  glass  which  it  contains.  When 
by  successive  ladings  the  cuvette  is  filled,  it  is  suffered  to  re¬ 
main  during  some  hours  in  the  furnace,  that  the  air-bubbles 
formed  by  this  disturbance  may  have  time  to  rise  and  disperse; 
an  effect  which  is  ascertained  to  have  ensued  by  the  inspection 
of  samples  withdrawn  from  time  to  time  for  the  purpose. 

Another  essential  part  of  the  apparatus  consists  in  flat  tables 
whereon  the  plates  of  glass  are  cast.  These  tables  have  per¬ 
fectly  smooth  and  level  metallic  surfaces,  of  suitable  dimen¬ 
sions  and  solidity,  supported  by  masonry.  At  St.  Gobain,  and 
formerly  also  at  Ravenhead,  these  tables  were  made  of  copper; 
the  reason  assigned  for  preferring  this  metal  being,  that  it  does 
not  discolor  the  hot  melted  glass,  while  the  use  of  iron  was 
thought  to  be  accompanied  by  this  disadvantage.  These  copper 
tables  were  very  costly,  both  from  the  nature  of  their  material, 
and  the  labor  bestowed  in  grinding  and  polishing  their  surfaces; 


;hap.  vi. 


PLATE  GLASS. 


159 


md  as  the  sudden  access  of  heat  that  accompanied  the  pouring 
>ver  them  of  such  a  torrent  of  melted  glass  occasioned  the 
netal  frequently  to  crack,  the  tables  were  by  such  an  accident 
•endered  useless.  The  British  Plate  Glass  Company  having 
experienced  several  disasters  of  this  nature,  its  directors  detdV- 
nined  upon  making  trial  of  iron ;  and  they  accordingly  pro¬ 
cured  a  plate  to  be  cast,  fifteen  feet  long,  nine  feet  wide,  and 
cix  inches  thick,  which  has  fully  answered  the  intended  purpose 
—having,  during  several  years  of  constant  use,  stood  uninjured 
hrough  all  the  sudden  and  violent  alternations  of  temperature 
,o  which  it  has  been  exposed.  This  table  is  so  massive,  weigh- 
ng  nearly  fourteen  tons,  that  it  became  necessary  to  construct 
i  carriage  purposely  for  its  conveyance  from  the  iron  foundery 
,o  the  glass-house.  It  is  supported  on  casters,  for  the  conveni¬ 
ence  of  readily  removing  it  towards  the  mouths  of  the  different 
innealing  ovens. 

The  foundery  at  Ravenhead  wherein  this  table  is  used  is  said 
,o  be  the  largest  room  under  one  roof  that  has  ever  yet  been 
erected  in  this  kingdom ;  it  is  339  feet  long,  155  wide,  and  pro¬ 
portionately  lofty.  Westminster  Hall,  to  which  the  superiority 
n  this  respect  is  so  commonly  ascribed,  is  smaller — its  length 
peing  300,  and  its  breadth  only  100  feet.  The  melting  fiir- 
paces,  which  are  ranged  down  the  centre,  occupy  about  one 
bird  of  the  whole  area  of  this  apartment.  The  annealing  ovens 
ire  placed  in  two  rows,  one  on  each  side  of  the  foundery,  and 
pccupy  the  greatest  proportion  of  the  side  walls.  Each  of  these 
pvens  is  sixteen  feet  wide  and  forty  feet  deep.  Their  floors 
peing  level  with  the  surface  of  the  casting  table,  the  plates  of 
2[lass  may  be  deposited  in  them  immediately  after  they  are  cast, 
ivith  little  difficulty  and  without  delay. 

When  the  melted  glass  in  the  cuvette  is  found  to  be  in  the 
2xact  state  that  experience  has  pointed  out  as  being  most  fa¬ 
vorable  for  its  flowing  readily  and  equably,  this  vessel  is  with- 
Irawn  from  the  furnace  by  means  of  a  crane,  and  is  placed 
upon  a  low  carriage,  in  order  to  its  removal  to  the  casting  table, 
which,  as  it  is  previously  placed  contiguous  to  the  annealing 
pven  that  is  to  be  filled,  may  therefore  be  at  a  considerable  dis¬ 
tance  from  the  melting  furnace.  Measures  are  then  taken  for 
cleaning  the  exterior  of  the  crucible,  and  for  carefully  removing 
with  a  broad  copper  sabre  any  scum  that  may  have  formed  upon 
the  surface  of  the  glass,  as  the  mixture  of  any  of  these  foreign 
natters  would  infallibly  spoil  the  beauty  of  the  plate.  These 
lone,  the  cuvette  is  wound  up  to  a  sufficient  height  by  a  crane ; 
md  then,  by  means  of  another  simple  piece  of  mechanism,  is 
swung  over  the  upper  end  of  the  casting  table ;  and  being 
thrown  into  an  inclined  position,  a  torrent  of  melted  glass  is 


160 


GLASS  MANUFACTURE. 


CHAT.  VI. 


The  glass  is  prevented  from  running  off  the  sides  of  the  tabic 
by  ribs  of  metal,  one  of  which  is  placed  along  the  whole  lenoth 
of  each  side,  their  depth  being  the  exact  measure  which  it  is 
desired  to  give  to  the  thickness  of  the  glass.  A  similar  rib,  at¬ 
tached  to  a  cross  piece,  is  temporarily  held,  during  the  casting, 
at  the  lower  end  of  the  table.  When  the  whole  contents  of 
the  crucible  have  been  delivered,  a  large  hollow  copper  cylin¬ 
der,  which  has  been  made  perfectly  true  and  smooth  in  a  turn¬ 
ing-lathe,  and  which  extends  entirely  across  the  table,  resting 
on  the  side  ribs,  is  set  in  motion ;  and  the  glass,  during  its  pro¬ 
gress,  is  spread  out  into  a  sheet  of  uniform  breadth  and  thick¬ 
ness.  Its  length  depends  upon  the  quantity  of  melted  glass 
contained  in  the  cuvette :  should  this  be  more  than  is  needed 
for  the  formation  of  a  plate  having  the  full  dimensions  of  the 
table,  the  metal  rib  is  removed  from  its  lower  part,  and  the  sur¬ 
plus  glass  is  received  in  a  vessel  of  water  placed  under  the  ex¬ 
treme  end  for  the  purpose. 

Mr.  Parkes,  in  speaking  of  this  operation,  remarks — “  The 
spectacle  ot  such  a  vast  body  of  melted  glass  poured  at  once 
from  an  immense  crucible,  on  a  metallic  table  of  great  magni¬ 
tude,  is  truly  grand ;  and  the  variety  of  colors  which  the  plate 
exhibits  immediately  after  the  roller  has  passed  over  it,  renders 
this  an  operation  far  more  splendid  and  interesting  than  can 
possibly  be  described.” 


suddenly  poured  out  on  the  surface  of  the  table,  which  must 
previously  have  been  heated,  and  wiped  perfectly  clean. 


Fig.  12. 


PLATE  GLASS. 


161 


CIIAP.  VI. 

At  least  twenty  workmen  are  busily  employed  during  this 
process  of  casting.  From  the  time  that  the  cuvette  is  removed 
from  the  furnace,  to  the  completion  of  the  casting  by  the  hard¬ 
ening  of  the  glass,  the  apartment  must  be  kept  as  free  as  pos¬ 
sible  from  disturbance ;  even  the  opening  and  shutting  of  a  door 
might,  by  setting  the  air  in  motion,  disturb  the  surface  of  the 
i  glass,  and  thus  impair  the  value  of  the  plate.  So  soon  as  it  is 
completely  set,  the  plate  is  carefully  inspected ;  and  should  any 
flaws  or  bubbles  appear  upon  any  part  of  its  surface,  it  is  im¬ 
mediately  divided  by  cutting  through  them. 

When  the  plate  of  glass  thus  formed  has  been  sufficiently 
fixed  by  cooling,  it  is  slipped  from  the  table  gradually  and  care¬ 
fully  into  one  of  the  annealing  ovens,  where  it  remains  in  a 
horizontal  position ;  its  treatment  differing  in  this  respect  from 
that  pursued  with  crown  and  broad  glass,  which  stand  on  edge 
during  the  annealing  process.  As  each  oven  in  this  manner 
becomes  filled,  it  is  closed  up  by  an  iron  door,  the  crevices  of 
-which  are  carefully  stopped  with  mortar  or  clay,  to  prevent 
any  access  of  external  air  to  the  oven;  and  thus  to  provide  as 
far  as  possible  for  the  gradual  cooling  of  the  plates,  the  neces¬ 
sity  for  which  has  already  been  sufficiently  explained.  When 
'the  glass  has  remained  during  about  fifteen  days  in  these  ovens, 
they  are  opened,  and  the  contents  withdrawn. 

The  plates  have  then  to  undergo  all  the  operations  of  squa¬ 
ring,  grinding,  polishing,  and  silvering,  in  order  to  fit  them  for 
sale. 

The  first  process— that  of  squaring  and  smoothing  the  edges 
! — is  performed  by  passing  a  rough  diamond  along  the  surface 
of  the  glass,  guided  by  a  square  rule ;  the  diamond  cuts  to  a 
certain  depth  "into  the  substance,  when,  by  gently  striking  the 
glass  with  a  small  hammer  underneath  the  part  which  is  cut, 
the  piece  comes  away  ;  and  the  roughnesses  of  the  edge  thus 
left  are  removed  by  pincers.  The  plate  is  then  taken  to  the 
[  grinding  apartment. 

The  next  step  is  to  embed  each  of  the  plates  upon  a  table  or 
frame  adjusted  horizontally,  and  made  of  either  freestone  or 
wood,  cementing  the  glass  securely  thereto  by  plaster  of  Paris. 
One  plate  being  then  reversed  and  suspended  over  another,  the 
material  employed  in  grinding  their  surfaces  is  introduced  be¬ 
tween  the  two,  and  they  are  made  to  rub  steadily  and  evenly 
upon  each  other  by  means  of  machinery  set  in  motion  by  a 
!  steam-engine.  It  was  formerly  usual  to  employ  river  sand  and 
water,  for  the  purpose  of  abrading  the  surfaces ;  a  circumstance 
which  entailed  considerable  waste  and  loss  upon  the  manufac¬ 
turers.  The  glass  which  was  ground  oft,  and  which  usually 
amounts  to  one  half  the  weight  of  the  plates  as  they  are  cast, 

O  2 


162  GLASS  MANUFACTURE.  CHAP.  VI. 

being  thus  mixed  with  a  material  which  contained  a  portion  of 
iron,  was  sold  at  a  low  rate  for  making  bottle  glass,  or  for 
scouring  pewter.  Mr.  Parkes  has  calculated  that  the  loss  of 
glass  by  this  means  to  one  establishment — that  which  was  car¬ 
ried  on  in  East  Smithfield — amounted  to  two  tons  weekly  ;  and 
that  the  expenditure  of  sand  in  the  same  period  was  at  least 
sixteen  to  twenty  tons. 

A  method  has,  however,  been  devised  for  saving  the  whole 
of  this  glass,  so  as  to  render  it  available  for  the  manufacture 
of  the  better  descriptions.  This  plan  consists  in  substituting, 
for  the  river  sand  before  mentioned,  ground  flints,  which  con¬ 
tain  no  portion  of  iron.  A  further  great  advantage  attending 
this  method  is,  that  one  ton  of  ground  flints  is  equally  effective 
with  five  tons  of  sand,  and  that  the  operation  is  completed  in  a 
shorter  time  than  formerly. 

When  one  side  of  each  plate  has  been  sufficiently  ground,  it 
is  loosened  from  the  frame,  and  turned  over,  so  as  to  present 
the  other  surface  to  be  ground  in  the  same  manner.  Some  de¬ 
gree  of  pressure  is  employed,  by  loading  the  upper  plate  with 
weights  as  the  grinding  of  each  side  approaches  to  completion. 
The  process  thus  described  used  formerly  to  last  during  three 
entire  days,  but  this  time  is  now  much  abridged.  The  greatest 
attention  is  required,  in  order  to  finish  with  the  surfaces  per¬ 
fectly  level  and  parallel,  for  which  end  a  rule  and  plumb  line 
are  employed. 

By  means  of  this  grinding,  the  plates  will  have  been  made 
level,  and  all  inequalities  in  the  surface  will  have  been  re¬ 
moved  ;  but  they  are  too  rough  to  receive  a  polish :  to  fit  them 
for  this,  they  must  again  be  ground  with  emery  powder  of  in¬ 
creasing  degrees  of  fineness.  The  preparation  and  sorting  of 
this  powder  are  effected  in  the  following  simple  and  ingenious 
manner : — 

A  considerable  quantity  of  emery  is  put  into  a  vessel  con¬ 
taining  water,  and  is  stirred  about  violently  until  the  whole  is 
mechanically  mixed  with  the  water.  Emery  is  absolutely  in¬ 
soluble  by  such  means;  and  if  the  mixture  were  left  at  l'est 
during  a  sufficient  time,  the  whole  would  subside  in  layers; 
the  coarsest  and  heaviest  particles  sinking  first,  and  so  on  suc¬ 
cessively,  until  the  very  finest  particles  would  range  themselves 
as  the  upper  stratum.  Previously  to  this,  however,  and  while 
these  finest  grains  are  still  suspended  in  the  water,  it  is  poured 
off  into  a  separate  vessel,  and  the  emery  is  there  allowed  to 
settle.  A  fresh  supply  of  water  is  poured  into  the  first  vessel, 
the  contents  of  which  are  again  violently  agitated,  and  allowed 
partially  to  subside  as  before.  A  shorter  interval  is  allowed  for 
this  than  in  the  first  case ;  and  then  the  liquor  is  poured  off  into 


CHAP.  VI. 


PLATE  GLASS. 


163 

a  third  vessel,  by  which  means  emery  of  the  second  degree  of 
fineness  is  separated.  This  operation  is  repeated,  in  order  to 
obtain  powders  having  four  different  degrees  of  fineness :  the 
deposits  are  then  separately  dried  upon  a  stove  to  a  consistence 
proper  for  making  them  up  into  small  balls,  in  which  form  they 
are  delivered  to  the  workman. 

In  this  further  rubbing  together,  or,  as  it  is  called,  smoothing 
of  the  glass  plates,  it  must  be  understood  that  the  coarsest 
emery  is  first  used,  and  so  on,  substituting  powders  having  in¬ 
creasing  degrees  of  fineness  as  the  work  proceeds.  ° 

This  operation  completed,  the  glass  is  perfectly  even ;  and 
although  the  surfaces  appear  opaque  or  deadened,  they  are  so 
smooth  that  no  scratchiness  is  at  all  perceptible.  The  plates 
are  now  again  subjected  to  a  rigid  examination ;  and  should  any 
flaws  or  defects  be  perceptible  in  them,  which  had  before  es¬ 
caped  detection,  they  are  cut  up  with  a  diamond  into  smaller 
plates,  so  that  the  blemishes  are  left  at  their  edges ;  regard  be¬ 
ing  had  to  economy  in  dividing  the  glass,  so  as  to  produce  the 
smallest  possible  number  of  pieces.  Attention  to  this  circum¬ 
stance  is  of  the  greatest  importance  to  the  profitable  working 
rf  the  establishment,  since  the  value  of  smaller  plates  bears  no 
comparison  with  that  of  glasses  having  more  considerable  di- 
nensions.  This  may  be  seen  at  once  in  referring  to  the  fol- 
owing  table,  which  has  been  calculated  upon  some  of  the  pub- 
ished  prices  of  the  British  Plate  Glass  Company. 


Dimensions. 

Surface  in  Square 
Inches. 

Price. 

Price  per 
Sq.  Inch. 

60  inches  by  30  inches. 

1,800 

£ 

10 

5. 

10 

d. 

1 

d. 

1-400 

60  -  - 

- 

40  - 

- 

2,400 

16 

3 

5 

1-617 

60  -  - 

- 

50  - 

- 

3,000 

22 

10 

5 

1-800 

70  -  - 

- 

50  - 

- 

3,500 

28 

7 

8 

1-946 

80  -  - 

- 

50  - 

- 

4,000 

34 

14 

10 

2-085 

100  -  - 

- 

50  - 

- 

5,000 

48 

9 

8 

1-327 

100  -  - 

- 

60  - 

- 

6,000 

63 

15 

1 

2-550 

100  -  - 

- 

70  - 

- 

7,000 

80 

8 

2 

2-757 

100  -  - 

- 

80  - 

- 

8,000 

98 

4 

10 

2-947 

132  -  - 

- 

84  - 

- 

11,088 

200 

8 

0 

4-337 

160  -  - 

- 

80  - 

- 

12,800 

246 

15 

4 

4-705 

The  largest  of  the  plates  here  mentioned  is  capable  by  reduc- 
ion  of  being  converted  into  7|  plates  having  the  dimensions  of 
lie  smallest  in  the  Table  ;  whereas  the  price  of  the  former  is 
!3-|  times  greater  than  that  of  each  of  the  small  plates,  and 


GLASS  MANUFACTURE. 


CHAP.  VI.! 


164 

more  than  3^  times  the  aggregate  value  of  those  into  which  it 
would  be  divided. 

The  reason  for  this  progressional  rate  in  the  prices  is  suffi¬ 
ciently  obvious.  Could  such  a  degree  of  perfection  be  attained 
in  the  different  processes  of  manufacture,  that  a  certainty  ex¬ 
isted  of  producing  plates  of  every  requisite  dimension,  there: 
would  no  longer  be  any  pretence  for  thus  enhancing  the  prices' 
of  the  larger  pieces ;  and  plates  might  be  sold  indiscriminately 
at«o  much  per  superficial  foot  in  the  manner  usual  with  linen; 
or  woollen  fabrics,  making  perhaps  some  allowance  for  the 
greater  expensiveness  of  machinery  required  for  large  than  for1 
small  operations.  But  such  a  degree  of  certainty  is  so  far  from, 
accompanying  the  labors  of  the  glass-founder,  that  it  is  but  very 
rarely  he  is  enabled  to  finish  and  produce  for  sale  any  plates  of  j 
extra  dimensions ;  while  it  most  frequently  happens  that  the 
presence  of  numerous  flaws  and  bubbles  compels  the  division 
and  subdivision  of  the  glass  into  portions  bearing,  for  the  very 
reason  of  their  abundance,  only  a  small  relative  value.  .  i 

It  is  represented  as  being  an  interesting  sight  to  witness  the; 
grinding  and  smoothing  of  a  great  number  of  plates  of  large 
dimensions,  which  by  means  of  machinery  are  thus  made  to 
move  with  great  velocity,  and  in  all  directions. 

The  next  process  is  that  of  polishmg.  For  this  purpose  a' 
substance  is  used,  known  in  commerce  and  the  arts  as  colcothar 
or  crocus  martis.  This  is  the  brown  red  oxide  of  iron,  which 
remains  in  the  retorts  after  the  distillation  of  the  acid  from 
sulphate  of  iron. 

The  instrument  used  in  polishing  is  a  piece  of  wood  covered 
with  many  folds  of  woollen  cloth,  each  fold  having  between  it 
some  carded  wool,  so  that  the  whole  forms  a  tolerably  hard  but 
elastic  cushion ;  and  this  is  furnished  with  a  handle  for  the  con¬ 
venience  of  the  workman. 

The  plate  is  embedded  in  plaster  upon  the  table  in  the  man¬ 
ner  already  described,  and  the  polishing  instrument  being  wet¬ 
ted  by  means  of  a  brush,  and  covered  with  colcothar,  the  work¬ 
man  commences  his  operation  by  rubbing  the  cushion  backward 
and  forward  over  the  surface  of  the  plate ;  not,  indeed,  attempt¬ 
ing  to  polish  the  entire  surface  at  the  same  time,  but  operating 
upon  separate  portions,  beginning  at  each  corner,  and  proceed¬ 
ing  regularly  towards  the  centre,  so  as  to  leave  no  part  unvis¬ 
ited  by  its  due  degree  of  attention  and  labor. 

Considerable  dexterity  and  practical  skill  are  needed,  not 
only  to  produce  a  high  polish  upon  the  plate,  but  also  to  give 
this  in  an  uniform  degree  over  its  whole  surface ;  and  the 
finishing  touches  require,  therefore,  to  be  given  with  great  care 
and  judgment. 


CHAP.  VI.  PLATE  GLASS.  165 

When  one  side  is  polished,  the  plate  is  turned  on  the  table, 
as  it  has  before  been  in  grinding  and  smoothing ;  but  as  the 
white  plaster  would  appear  through  the  glass  and  hinder  the 
workman  from  forming  an  accurate  judgment  upon  his  progress 
in  this  second  operation,  the  previously  polished  side  is  provided 
with  a  coating  of  red  colcothar.  When  the  workman  is  satis¬ 
fied  with  the  result  of  his  labor  upon  this  second  surface,  the 
plate  is  taken  from  the  table,  and  being  cleaned,  is  laid,  each 
side  in  its  turn,  upon  a  dark  biue  or  black  cloth,  which,  as  it 
admits  only  a  moderate  light,  show's  by  inspection  any  parts 
which  may  be  less  elaborately  polished  than  the  rest :  these 
must  be  retouched  by  a  small  polishing  cushion,  in  the  same 
manner  as  before. 

It  would  be  a  tedious  operation,  if  every  small  fragment  of 
glass,  such  pieces,  for  instance,  as  are  used  in  swing  frames  on 
toilet-tables,  must  be  polished  separately.  The  edges  of  several 
of  these  pieces  are  therefore  brought  together  for  the  purpose  ; 
but  as  all  these  are  not  of  one  uniform  thickness,  it  is  necessary 
to  remedy  this  inconvenience  ;  and,  in  order  to  bring  their  sur¬ 
faces  to  a  perfect  level,  they  are  arranged,  with  the  side  to  be 
polished  downwards,  on  a  large  smooth  level  plate  ;  plaster  of 
Paris  is  then  poured  upon  their  upper  surfaces,  which  are  thus 
embedded  together,  and  on  being  turned  over,  the  whole  num¬ 
ber  of  pieces  is  found  to  be  so  level,  that  the  polishing  may  be 
performed  as  easily  and  as  effectually  as  it  could  be  with  one 
entire  plate. 

When  the  polishing  of  the  plates  has  been  satisfactorily  com¬ 
pleted,  they  are  washed  with  water,  and  are  either  removed  to 
the  ware-room  for  sale,  or,  in  case  of  their  being  intended  for 
mirrors,  to  the  silvering  apartment. 

The  last  process  used  in  a  plate-glass  manufactory  is  that 
which  is  called  silvering.  This,  in  common  with  the  greater 
part  of  the  operation  connected  with  this  branch  of  the  art,  is 
simple,  but  requires  practice  and  dexterous  management  for  its 
proper  performance.  The  application  to  the  posterior  surface 
ff  mirrors  of  some  substance  that  will  accurately  reflect  the 
rays  of  light  falling  upon  them,  is  absolutely  necessary  to  ren- 
ler  them  useful.  The  substance  which  has  been  found  to  an¬ 
swer  this  purpose  best  is  mercury ;  which,  as  it  cannot  be  aj> 
alied  alone  in  its  fluid  state,  is,  by  a  partial  amalgamation,  pre¬ 
viously  made  to  adhere  to  the  surface,  and  afterwards  to  incor¬ 
porate  itself  with  the  substance  of  a  very  thin  leaf  of  tinfoil. 

The  operation  is  thus  conducted : — A  perfectly  flat  and 
smooth  slab  of  thick  wood,  or  of  stone,  somewhat  larger  than 
my  plate  which  it  may  be  required  to  silver,  must  be  inclosed 
within  a  wooden  frame  open  at  the  top,  and  having  a  ledge  a 


166 


GLASS  MANUFACTURE. 


CHAP.  VI. 


few  inches  deep  round  three  of  its  sides.  The  bottom  of  this 
frame  is  provided  with  a  channel  to  collect  the  surplus  mer¬ 
cury,  and  to  convey  it  to  a  vessel  placed  underneath.  The  slab 
is  fixed  on  a  pivot,  so  that  one  end  may  be  raised  and  the  other 
depressed  at  pleasure. 

When  it  is  used,  the  slab  must  first  he  adjusted  horizontally, 
and  covered  with  gray  paper  stretched  tightly  over  it.  A  sheet 
of  very  thin  tinfoil,  a  little  larger  than  the  plate  to  be  silvered, 
is  then  laid  smooth  upon  the  paper,  and  as  much  mercury  is 
poured  steadily  upon  it  as  will  remain  upon  its  flat  surface. 
That  end  of  the  slab  which  is  unprovided  with  a  ledge  is  then 
covered  with  parchment,  and  the  plate  of  glass  is  carefully  slid- 
den  into  the  frame,  resting  the  while  upon  the  parchment. 

The  art  of  properly  effecting  this  deposit  of  the  glass  upon 
the  foil  consists  in  holding  it,  during  its  sliding,  in  such  a  posi¬ 
tion  that  it  will  dip  into  the  mercury,  carrying  a  portion  of  the 
metal  before  it,  but  without  once  touching  the  tin  in  its  pas¬ 
sage.  By  this  means  any  dust  or  oxide  which  may  rest  upon 
the  mercury  will  be  removed,  and  no  air-bubbles  will  remain 
between  the  glass  and  the  foil ;  while,  if  the  tin  were  touched, 
however  slightly,  it  would  certainly  be  torn. 

When  the  entire  surface  of  the  glass  plate  has  thus  passed, 
it  is  allowed  gently  to  drop  on  the  tinfoil,  and  to  squeeze  out 
the  superfluous  mercury  from  between,  and  which  is  collected 
in  the  channel  already  mentioned.  The  plate  being  then  cov¬ 
ered  with  a  thick  flannel,  is  loaded  at  regular  intervals  of  space 
with  considerable  weights,  and  the  end  of  the  slab  is  a  little 
raised,  which  assists  the  escape  of  the  superabundant  mercury. 
The  whole  remains  in  this  situation  during  the  entire  day,  tire 
slope  of  the  slab  being  gradually  increased  to  facilitate  the 
dropping  of  the  mercury.  At  the  end  of  this  time,  the  plate 
is  cautiously  taken  from  the  frame,  carefully  avoiding  to  touch 
the  under  side,  then  covered  uniformly  with  a  soft  amalgam  of 
tin  and  mercury.  The  plate  is  then  placed  in  a  wooden  frame, 
and  left  during  several  days  until  the  amalgam  is  found  to  be 
so  far  hardened  as  to  adhere  with  a  great  degree  of  firmness 
to  the  glass  :  in  this  state  not  even  a  slight  scratch  would  suf¬ 
fice  for  its  removal.  The  plate  is  then  in  a  finished  state,  and 
fit  for  being  framed. 

The  amalgam  does  not,  however,  acquire  its  greatest  degree 
of  hardness  until  some  time  has  elapsed ;  and  globules  of  Mer¬ 
cury  will  occasionally  drop  from  mirrors  for  some  time  even 
after  they  have  been  framed.  Portions  of  the  amalgam  are  at 
times  detached  while  in  this  state,  by  violent  concussions  of  the 
air,  such  as  a  thunder  storm,  or  the  firing  of  artillery.  No 
patching  can  ever  be  applied  in  such  a  case  that  will  be  suffi' 


CHAP.  VI.  PLATE  GLASS.  1G7 

Gently  perfect  to  escape  detection ;  but  a  white  seam  will  in¬ 
variably  be  perceptible  at  the  points  of  junction. 

Although  the  processes  followed  in  blowing  plate  glass  are, 
n  most  respects,  similar  to  those  used  in  fashioning  broad  glass, 
some  difference  is  yet  observed ;  which,  indeed,  is  occasioned 
is  much  through  the  increased  bulk  and  weight  of  the  mass 
rnder  operation,  as  on  account  of  any  real  difference  in  the 
composition  of  the  fabrics ;  only  a  very  short  account  of  the 
irocess  can  therefore  be  required. 

The  first  instrument  used  is  a  hollow  rod,  agreeing  in  every 
articular,  except  its  size,  with  that  used  for  forming  flint  and 
crown  glass.  This  rod  is  full  six  feet  in  length,  and  two  inches 
n  diameter ;  made  smaller  at  the  end  to  which  the  breath  is 
applied,  and  widened  at  the  extremity  upon  which  the  glass  is 
gathered.  It  is  necessary  to  take  up  a  considerable  weight  of 
flass  upon  this  tube ;  and  some  management  is  required  in 
irder  to  effect  this.  When  the  workman  has  gathered  all 
hat  will  adhere  by  turning  the  end  continually  round  in  the 
'ot,  he  then  withdraws  it  from  the  furnace;  and  holding  it 
ver  a  bucket  of  water,  sprinkles  the  glass  on  the  end  of  "the 
ube,  turning  it  constantly  round  in  his  hand.  When  cooled  in 
his  manner,  the  glass  adheres  firmly  to  the  tube,  and  is  rendered 
■y  that  means  capable  of  sustaining  a  greater  weight  than  it 
vould  otherwise  support.  The  tube  is  then  dipped  again  into 
he  pot,  and  the  same  process  is  repeated. 

Fig.  13. 


After  the  third  dipping  it  will  have  gathered  a  mass  of  glass 
n  the  shape  of  a  pear,  ten  inches  in  diameter,  and  about 
welve  inches  long.  This  must  again  be  cooled  with  sprink- 
ing  as  before ;  and  while  the  workman  is  at  the  same  time 
ilowing  into  the  tube,  so  as  to  give  a  hollow  form  to  the  glass, 
aid  to  reduce  it  to  the  requisite  thickness,  the  rod  must  be 
cwung  to  and  fro  with  an  alternating  motion,  in  order  to  length¬ 
en  the  shape  of  the  material ;  and  this  proceeding  being  several 
imes  repeated,  the  glass  assumes  the  form  of  a  cylinder,  the 
ower  end  of  which  is  hemispherical. 

Fig.  14. 


168  GLASS  MANUFACTURE.  CHAP.  VI. 

The  assistant  is  then  placed  three  feet  and  a  half  from  the 
ground,  upon  a  stool,  whereon  are  fixed  two  upright  pieces  of 
wood,  with  a  cross  piece  of  the  same  material,  for  the  purpose 
of  supporting  the  tube  with  the  glass.  These  are  held  by  the 
assistant  in  an  oblique  position,  the  end  with  the  glass  inclin¬ 
ing  downwards,  that  the  workman  may  be  able,  with  an  iron 
punching  instrument  and  a  mallet,  to  drive  a  hole  through  the 
centre  of  the  hemispherical  end  of  the  cylinder. 


Fig.  15. 


The  glass  now  is  subjected  to  examination;  and  if  found 
sufficiently  free  from  imperfections,  is  held  at  the  aperture  of 
the  furnace  during  seven  or  eight  minutes  to  heat  it  again 
thoroughly.  While  thus  held,  the  rod  is  supported  in  its  hori¬ 
zontal  position  by  a  small  iron  trestle  placed  before  the  orifice 
of  the  furnace  conveniently  for  that  purpose.  The  glass  being 
thus  sufficiently  softened  by  heat,  the  assistant  is  again  mount¬ 
ed  upon  the  stool ;  and  resting  the  tube  upon  the  wooden  cross¬ 
piece,  twirls  it  round,  while  the  workman  insinuates  a  pair  of 
large  broad  shears  which  are  pointed  at  the  end,  into  the  hole 


Fig.  16. 


previously  punched.  This  is  gradually  enlarged,  until  the 
glass,  through  its  whole  length,  and  except  at  the  part  where 
it  is  attached  to  the  tube,  has  a  cylindrical  form. 


Fig.  17. 


The  tube  is  then  again  rested  on  the  trestle,  and  the  glass  is 
reheated  at  the  furnace,  when  the  shears  are  used  to  cut  the  cyl¬ 
inder  through  half  its  length,  beginning  at  the  open  end,  and 
proceeding  towards  the  point  where  it  is  attached  to  the  tube. 

Fig.  18. 


CHAP.  VI. 


PLATE  GLASS. 


169 


The  next  proceeding  is  to  take  a  pontil,  an  instrument  al¬ 
ready  described  as  being  a  solid  rod  of  iron  of  smaller  diameter 
than  the  tube,  from  which  last  the  glass  is  now  to  be  transferred 
to  the  pontil.  This  differs  from  the  instrument  used  for  the 
like  purpose  in  making  flint  glass,  by  having  an  iron  cross¬ 
piece,  twelve  inches  in  length,  placed  across  its  extreme  end, 
and  forming  with  it  the  letter  T.  The  pontil  being  thoroughly 
heated  at  the  end,  a  quantity  of  melted  glass  is  gathered  from 
the  pot  upon  the  cross-piece,  which  being  presented  to  the  diam¬ 
eter  of  the  cylinder,  the  two  cohere  speedily  and  firmly  to¬ 
gether  :  the  hollow  tube  is  then  disconnected  from  the  glass  in 
the  manner  already  described. 


Fig.  19. 


The  pontil  with  the  cylinder  is  now  rested  on  the  trestle, 
and  presented  to  the  furnace,  that  the  end  which  has  hitherto 
been  attached  to  the  tube  may  in  turn  be  heated  and  subjected 
to  the  same  processes  as  have  just  been  effected  with  the  other 
end  :  the  extremity  is  opened  by  introducing  the  shears  so  as 
to  complete  the  cylinder  {jig.  20.);  and  then  after  a  fresh 


Fig.  20. 


heating  the  workman  cuts  through  the  remaining  half  of  the 
length  of  the  cylinder  in  a  line  with  and  joining  to  the  cut 
already  mentioned,  so  that  the  cylinder  is  divided  on  one  of 
its  sides  through  its  entire  length. 


Fig.  21. 


The  glass  is  then  placed  with  the  cut  side  upwards  upon  an 
iron  shovel ;  it  is  separated  from  the  pontil,  and  immediately 
removed  to  the  hottest  part  of  the  annealing  oven,  where  it 
gradually  becomes  again  heated  to  redness.  Advantage  is 
then  taken  of  the  softened  state  of  the  cylinder  to  open  it,  by 
the  help  of  an  appropriate  iron  instrument,  lifting  up  and  turn¬ 
ing  back  the  cut  edges  of  the  glass,  until  the  whole  is  flattened 
upon  the  hearth  of  the  annealing  oven.  A  small  iron  rake  is 
then  employed  to  push  the  plate  along  the  floor  to  the  end  of 

P 


GLASS  MANUFACTURE. 


CHAP.  VI. 


170 


the  oven ;  and  when  this  lias  been  filled  through  a  succession 
of  operations  such  as  are  here  described,  the  door  is  stopped 

Fig.  22. 


and  cemented.  All  further  processes  are  in  every  respect  the' 
same  as  are  followed  with  plates  that  have  been  cast. 

The  great  size  and  weight  of  the  glass  render  these  opera¬ 
tions  exceedingly  laborious,  so  that  a  man  and  his  assistant  can 
hardly  do  more  than  make  one  plate  in  an  hour,  nor  can  they 
continue  their  labor  longer  than  six  hours,  resting  during  an 
equal  space  before  they  resume  their  toil. 

Plates  which  are  blown  cannot  properly  be  made  above  forty- 
five,  or  at  most  fifty,  inches  in  length,  and  with  a  proportionate 
breadth.  They  have  sometimes  been  made  larger,  but  are 
then  too  thin  to  admit  of  their  properly  bearing  the  processes 
of  grinding  and  polishing,  and  are  besides  liable  to  warp,  which 
of  course  destroys  their  value  when  employed  as  mirrors. 

It  was  long  since  observed,  that  by  exposing  plate  glass  to 
the  solar  rays,  it  is  made  to  acquire  a  violet  or  purple  tinge, 
and  this  so  rapidly,  that  the  alteration  is  clearly  discernible  at 
the  end  of  one  or  two  years.  Some  plates,  originally  colorless, 
which  had  thus  become  tinged,  having  been  brought  under  the 
notice  of  Mr.  Faraday,  he  was  induced  to  experiment  upon  the 
subject  For  this  purpose,  he  procured  three  different  pieces 
of  plate  glass,  which  were  tinged  so  slightly  as  to  appear  alto¬ 
gether  colorless,  unless  when  viewed  through  their  edges. 
Each  of  these  pieces  was  broken  into  two  portions,  one  of 
which  was  wrapped  in  paper,  and  set  aside  in  a  dark  place  \ 
while  the  portion  from  which  it  had  been  separated  was  ex¬ 
posed  to  the  air  and  the  light  of  the  sun.  This  exposure  was 
commenced  in  the  month  of  January ;  and  in  the  following  Sep¬ 
tember  a  comparative  examination  was  made.  The  pieces 
from  which  the  light  had  been  excluded  exhibited  no  sign  of 
change,  while  those  which  had  been  exposed  had,  in  this  short 
space  of  eight  months,  acquired  so  considerable  a  degree  of 
color  as  would,  under  other  circumstances,  have  created  a 
doubt  regarding  their  original  identity. 


CHAP.  VII. 


ARTIFICIAL  GEMS. 


171 


CHAPTER  VII. 

ON  THE  COMPOSITION  OF  ARTIFICIAL  GEMS. 

Great  interest  formerly  attached  to  this  subject. — Different  Compositions 
for  Artificial  Gems. — Mode  of  Preparation. — Rock  Crystal  formerly  em¬ 
ployed. — Not  superior  to  Sand. — Diamond  Pastes. — Selection  of  various 
Pastes  for  Imitating  different  Gems. — Reasons  for  such  selection. 

A  very  considerable  portion  of  every  treatise  on  glass-ma¬ 
king,  which  was  in  existence  a  century  ago,  and  which  com¬ 
prises  nearly  the  whole  of  what  has  ever  been  published  on  the 
subject,  was  devoted  to  the  art  of  composing  factitious  gems. 
A  great  deal  of  mystery  would  seem  to  have  been  affected 
upon  this  subject  on  the  part  of  the  manufacturers,  each  one  of 
whom  was,  or  pretended  to  be,  possessed  of  some  secret  recipe , 
which  he  thought  superior  to  all  others  for  the  composition  of 
these  ornaments. 

A  corresponding  anxiety  to  acquire  a  knowledge  of  these 
mysteries  being  evinced  on  the  part  of  the  public,  the  authors 
above  alluded  to,  so  far  acquiesced  in  this  feeling  as  to  load 
their  writings  with  one  receipt  after  another,  in  almost  endless 
succession,  and  in  following  which  the  artist  was  assured,  that 
he  might  successfully  rival  nature  in  the  production  of  these 
much-admired  objects. 

The  greater  part  of  the  compositions  thus  recommended,  if 
indeed  they  were  ever  used,  has  long  since  passed  into  neg¬ 
lect  ;  and  it  will  not  be  necessary,  in  the  present  day,  to  insert 
more  than  a  very  few  directions  on  the  subject,  which  are  given 
upon  the  authority  of  M.  Fontanieu,  as  being  well  qualified, 
with  the  addition  of  various  coloring  matters,  for  counterfeiting 
precious  stones. 

No.  1.  is  composed  of  20  parts  of  litharge,  12  of  silex,  4  of 
nitre,  4  of  borax,  and  2  parts  of  white  arsenic.  These  ingre¬ 
dients  should  be  fritted  together  in  a  crucible,  and  afterwards 
melted,  in  which  state  the  whole  must  be  poured  suddenly  into 
cold  water.  Any  portion  of  lead  which  may  have  been  revived 
in  the  metallic  state  will  then  be  apparent  and  must  be  separa¬ 
ted.  The  glass  may  then  be  remelted  for  use. 

No.  2.  For  this  composition,  mix  together  20  parts  of  ceruse, 
8  of  silex  in  powder,  4  of  carbonate  of  potash,  and  2  of  borax. 
When  these  are  perfectly  melted,  the  whole  should  be  poured 
into  water,  and  then  remelted  in  a  clean  crucible,  in  the  same 
manner  as  No.  1. 

No.  3.  consists  of  16  parts  of  minium,  8  of  rock  crystal  in 
powder,  4  of  nitre,  and  4  of  carbonate  of  potash.  These  ingl'e- 


172 


GLASS  MANUFACTURE. 


CHAP.  VII. 


dients  must  be  melted  and  remelted  in  the  manner  already  de¬ 
scribed  as  necessary  with  the  preceding  mixtures. 

No.  4  differs  essentially  from  the  three  foregoing  combina¬ 
tions  in  being  without  any  portion  of  lead.  It  is  made  with  24 
parts  of  borax,  8  parts  of  rock  crystal,  and  8  of  carbonate  of 
potash.  The  rock  crystal,  previous  to  its  use  for  this  purpose, 
must  be  reduced  to  a  state  of  great  purity,  by  fusing  it  with  an 
excess  of  alkali,  and  then  precipitating  it  by  an  excess  of  acid, 
in  the  form  of  an  impalpable  powder. 

No.  5.  The  processes  necessary  for  the  production  of  this 
species  of  glass  are  much  more  complex  than  the  preceding.  In 
the  first  place,  3  parts  of  alkali  are  to  be  fritted  with  1  part  of 
rock  crystal,  which  mixture  must  then  be  dissolved  in  water 
and  saturated  with  dilute  nitric  acid.  The  silex  which  is  pre¬ 
cipitated  by  this  means  must  then  be  edulcorated  and  dried, 
when  it  will  appear  in  the  form  of  a  very  fine  impalpable  pow¬ 
der.  Two  parts  of  this  must  be  melted  in  a  crucible  with  3 
parts,  by  weight,  of  the  best  ceruse,  and  the  glass  which  re¬ 
sults  must  be  poured  into  water.  Break  this  down  and  remelt 
it  with  one  twelfth  of  its  weight  of  borax,  and  pour  it  again  into 
water.  If  this  last  product  is  once  more  melted  with  one  twelfth 
of  its  weight  of  nitre,  the  result  will  be  a  very  fine  hard  glass, 
having  an  extremely  beautiful  lustre. 

The  length  of  time  required  for  fusing  hard  glasses  or  pastes 
is  at  the  least  twenty-four  hours.  The  process  herein  directed, 
of  pouring  the  melted  glass  into  water,  and  then  remelting,  is 
found  to  be  of  considerable  use  in  thoroughly  and  intimately 
mixing  the  ingredients  together. 

Of  the  foregoing  compositions,  No.  1.  will  be  found  extreme¬ 
ly  fusible,  on  account  of  its  considerable  proportion  of  fluxing 
materials.  It  calls  for  the  employment  of  the  very  best  descrip¬ 
tion  of  crucibles,  in  order  to  withstand,  for  the  requisite  time, 
the  corroding  effects  of  the  mixture.  If  any  kind  of  glass  into 
the  composition  of  which  lead  has  not  entered,  is  applied  to  and 
melted  on  the  interior  surface  of  the  crucible,  so  as  to  line  it 
with  a  perfect  glaze  previous  to  use,  the  evil  just  mentioned 
will  be  materially  remedied. 

In  order  to  make  a  perfect  glass,  which  at  the  same  time 
shall  be  sufficiently  workable,  2  parts  of  silex  require  from  3  to 
4  parts,  by  weight,  of  oxide  of  lead ;  but  a  somewhat  smaller 
quantity  of  the  latter  may  be  used,  if  the  deficiency  is  made  up 
by  the  addition  of  some  other  fluxing  material :  the  glass  in 
this  case  will  prove  both  hard  and  brilliant ;  and,  when  proper¬ 
ly  set,  will  exhibit  a  much  nearer  imitation  of  the  diamond  than 
most  other  vitreous  compositions. 

It  was  formerly  imagined  by  artists  who  wrought  these  arti- 


CHAP.  VII. 


ARTIFICIAL  GEMS. 


173 


ficial  gems,  that  if  the  glass  employed  by  them  had  for  its  basis 
rock  crystal,  rather  than  sand,  flint,  or  any  other  mineral  of  the 
like  character,  the  result  was  a  much  harder  glass  than  ordi¬ 
nary.  This  idea  is,  however,  wholly  without  foundation ;  for 
when  the  crystal  has  once  been  fused  through  the  admixture 
of  any  kind  of  flux,  the  hardness  of  the  mineral  will  be  irrecov¬ 
erably  lost,  as  this  quality  depends  altogether  upon  its  natural 
aggregation,  which,  in  such  case,  is  necessarily  destroyed. 

Rock  crystal  is,  perhaps,  somewhat  purer  than  most  other 
siliceous  substances,  some  of  which  contain  minute  traces  of 
iron,  and  which  may  possibly  impair  the  beauty  of  some  colors 
which  are  imparted  to  glass.  The  same  means  as  are  used  to 
render  flint  friable,  are  employed  for  that  purpose  with  rock 
crystal:  this  should  on  no  account  be  ground  in  metallic 
vessels. 

Some  artists  have  succeeded,  to  a  certain  extent,  in  produ¬ 
cing  a  very  fine,  hard,  brilliant,  and  colorless  glass  paste,  in  im¬ 
itation  of  the  diamond,  and  have  even  given  to  this  a  very  con¬ 
siderable  play  of  light,  or,  as  it  is  technically  termed,  water ; 
but  it  has  not  been  found  practicable  to  compound  any  vitreous 
substance  which  could  for  a  moment  deceive  the  eye  of  any 
person  accustomed  to  witness  the  superior  brilliancy  of  real 
gems.  The  best  of  these  mock  diamonds  require,  indeed,  the 
aid  of  artifice  in  the  mode  of  their  setting,  to  render  them  in 
any  great  degree  ornamental.  M.  Fontanieu  recommends  his 
glass,  No.  1,  described  in  this  Chapter,  as  being  better  quali¬ 
fied  than  any  other  for  making  artificial  diamonds.  To  bring 
this  glass  to  such  a  degree  of  brilliancy  and  clearness  as  will 
prove  at  all  satisfactory,  it  must  be  retained  in  a  state  of  per¬ 
fect  fusion  for  a  considerable  space  of  time. 

Loysel  recommends,  for  the  same  purpose,  the  employment 
of  a  different  composition,  the  result  of  which  will  be  a  glass, 
having  the  same  specific  gravity  as  the  white  oriental  diamond, 
and  for  this  reason  better  imitating  that  resplendent  substance 
in  its  refractive  and  dispersive  powers.  His  recipe  is  as  fol¬ 
lows  : — 

White  sand  purified  by  being  washed  first 
in  muriatic  acid,  and  afterwards  in  pure 
water,  until  all  traces  of  the  acid  are 


removed . 100  parts. 

Red  oxide  of  lead  (minium) . 150 

Calcined  potash .  30  to  35 

Calcined  borax .  10 

Oxide  of  arsenic .  1 


This  composition  is  easily  fusible  at  a  moderate  heat ;  but  like 
that  proposed  by  Fontanieu,  requires  to  be  kept  in  a  melted 

P  2 


174 


GLASS  MANUFACTURE. 


CHAP.  VII. 


state  for  two  or  three  days,  to  perfect  the  refining,  and  to  cause 
the  dissipation  of  the  superabundant  alkali. 

The  same  author  has  furnished  the  following  receipts  for  the 
formation  of  pastes,  qualified,  upon  the  addition  of  appropriate 
coloring  materials,  for  the  imitation  of  various  gems.  The  re¬ 
marks  already  made  as  to  the  length  of  time  required  for  the 
due  preparation  of  the  diamond  paste  equally  apply  to  these 
compositions : — 

White  sand,  purified  in  the  manner  point¬ 
ed  out  in  the  preceding  receipt,  ....  100  parts. 

Red  oxide  of  lead . 200 

Calcined  potash,  and  nitre,  of  each  ....  20  to  25. 

The  specific  gravity  of  this  glass,  water  being  1,  will  be  3.9 
to  4. 

White  sand,  prepared  in  the  manner  be¬ 


fore  mentioned, . 100  parts. 

Red  oxide  of  lead, . 300 

Calcined  potash, .  5  to  10 

Calcined  borax, .  200  to  300 


The  specific  gravity  of  this  compound  will  vary  from  3-3  to  4. 


White  sand,  prepared  as  above, . 100  parts. 

Red  oxide  of  lead, . 250 

Calcined  potash, .  15  to  20 

Calcined  borax, .  25  to  30. 


This  will  have  a  greater  specific  gravity  varying  from  4  to 
4.5. 

In  making  his  selection  between  one  or  other  of  these  pastes, 
the  artist  should  be  guided  by  their  various  specific  gravities, 
choosing  preferably  that  glass  which  is  nearest  in  this  respect 
to  the  particular  gem  which  he  is  desirous  of  imitating ;  and 
this,  not  witli  the  view  of  providing  himself  with  an  additional 
means  of  deception,  but  because,  the  refractive  and  dispersive 
powers  of  different  transparent  bodies  being  determined  by 
their  comparative  weights,  the  resemblance  will,  by  such  a 
selection,  be  rendered  more  perfect  to  the  eye.  To  one  simple 
test,  that  of  their  hardness,  recourse  can  be  had  so  easily,  that 
every  one  may,  with  very  little  previous  instruction,  ascertain 
for  himself  the  genuineness  of  any  gem  that  is  offered  to  his 
notice,  without  any  apprehension  of  being  deceived. 


CHAP.  VIII. 


PHOSPHORIC  GLASS. 


175 


CHAP.  VIII. 


ON  THE  MANUFACTURE  OF  GLASS  FROM  CALCINED  BONES. 


Preparation  of  Bones. — Their  Vitrification.— Process  known  to  Becher _ 

Concealed  by  him.— Curious  Suggestion  as  to  its  Employment— This 
Glass  highly  electric  when  newly  made. 


Glass  may  be  made  from  calcined  bones  by  digesting-  them 
during  two  or  three  days  with  half  their  weight  of  sulphuric 
acid,  evaporating  to  dryness,  and  washing  the  residue  in  many 
different  waters,  until  all  the  soluble  matter  is  exhausted.  The 
production  of  this  effect  is  known  by  the  water  having  no 
longer  a  yellow  tinge. 

The  different  waters  thus  used  must  then  be  brought  to¬ 
gether  and  evaporated  to  afford  a  solid  extract.  To  separate 
the  sulphate  of  lime  contained  in  this,  the  extract  must  be  dis¬ 
solved  in  the  least  possible  quantity  of  water,  and  filtered:  the 
salt  will  then  remain  on  the  filter.  This  extract  may  be  mixed 
with  powdered  charcoal,  and  distilled  for  the  production  of 
phosphorus ;  but  if,  instead  of  this,  it  be  placed  in  a  large  cru¬ 
cible,  and  the  fire  is  urged,  it  will  at  first  swell  considerably, 
but  ere  long  will  again  settle,  and  at  that  instant  the  glass  is 
made.  This  is  white,  and  of  a  milky  color. 

These  directions  are  taken  from  the  System  of  Chemistry  of 
M.  Chaptal ;  who  tells  us  that  before  his  time  Becher  was  per¬ 
fectly  well  acquainted  with  the  use  to  which  bones  could  thus 
be  applied,  but  that  he  concealed  the  process,  on  account  of  the 
abuse  which,  according  to  his  apprehensions,  might  be  made  of 
t,  and  to  which  he  plainly  enough  alludes  in  the  words — “  IIo- 
no  vitrum  est,  et  in  vitrum  redigi  potest ;  sicut  et  omnia  ani- 
nalia.”  This  author  was,  nevertheless,  led  to  express  his  re¬ 
gret  that  the  Scythians,  who  drank  from  disgusting  skulls,  were 
lot  acquainted  with  the  art  of  converting  them  into  so  cleanly 
■  substance  as  glass ; — and  he  also  showed  the  possibility  of 
orming  a  gallery  of  family  effigies,  moulded  from  glass,  the 
•roduce  of  the  identical  bones  of  the  originals,  in  which  the 
ikenesses  might  be  preserved  as  truly  as  they  now  are  by  the 
mner.  M.  Chaptal  adds,  that  a  skeleton  of  nineteen  pounds1 
might  may  be  made  to  yield  five  pounds  of  this  phosphoric 
lass. 

Newly  made  glass  of  this  description  will  emit  very  strong 
metric  sparks,  which  will  fly  to  the  hand  at  the  distance  of  two 
iches :  but  this  property  ceases  after  one  or  two  days,  however 
j  irefully  the  glass  may  be  preserved  from  contact  with  the  at- 
'  osphere.  The  substance  is  in  fact  phosphoric  acid  which  has 


GLASS  MANUFACTURE. 


CHAP.  IX. 


176 


been  deprived  of  its  water,  and  which  if  not  carefully  preserved 
from  the  atmosphere  it  will  again  imbibe,  becoming  deliques¬ 
cent.  It  has  an  acid  taste,  and  is  soluble  in  water. 


CHAP.  IX. 

ON  THE  USE  MADE  OF  THE  BLOWPIPE,  AND  ON  VARIOUS  SMALL 
MANUFACTURES  OF  GLASS. 

Thermometer  Tubes. — Mode  of  giving  to  them  an  Elliptical  Bore.— Blowpipe 
and  Apparatus  described.— Materials  used.— Method  of  Working. — Seal¬ 
in'*  Tubes. — Bending  and  Joining  Tubes. — Bulbs. — Spun  Glass. — Watch- 
Glasses.— Lunette  Glasses.— Glass  Beads.— Manufactory  at  Murano.— 
Striped  Tubes.— Mode  of  forming  Beads.— Sorting  them.— Numerous  Kinds 
of  Beads.— Mock  Pearls.— Manner  of  their  Invention  and  formation.— Dial 
Plates.— How  formed.— Lettering  and  Figuring. 

A  considerable  number  of  articles  are  made  of  glass  with 
the  aid  of  a  lamp  and  blowpipe.  The  principal  of  these  articles, 
such  as  thermometers  and  barometers,  are  formed  from  tubes 
which  are  made  at  the  glass-houses,  of  different  bores  and  sub¬ 
stances,  by  drawing  out  quickly,  and  while  soft  with  heat,  a 
thick  and  short  tube  into  one  that  is  thin  and  long. 

The  method  of  performing  this  process  is,  to  gather  the  ne¬ 
cessary  weight  of  glass  upon  the  rod ;  and  this  glass  having: 
been  elongated  and  hollowed  by  the  workman’s  breath  in  the; 
usual  manner,  a  punt  is  attached  to  the  end  of  the  cylinder  op¬ 
posite  to  the  rod.  The  workman  then  holding  the  rod  and  his; 
assistant  the  punt,  each  proceeds  in  a  direction  opposite  to  that 
taken  by  the  other,  by  which  means  the  tube  is  elongated  in 
the  necessary  degree ;  and  being  then  made  to  rest  upon  billets 
of  wood  placed  horizontally  and  parallel  to  each  other  at  equal 
distances  on  the  ground,  it  speedily  cools,  and  may  in  that  state: 
be  readily  cut  into  convenient  lengths. 


Fig.  23, 


Whatever  may  be  the  original  form  of  this  tube  and  of  its 
perforation,  it  is  found  that  the  same  form  will  be  relatively 
continued  throughout  the  entire  length  to  which  it  is  drawn 
out  If  its  perforation  be  at  first  cylindrical,  it  will  so  continue] 


UP.  IX.  BLOWPIPE.  177 

rntever  degree  of  length  and  minuteness  it  may  be  made  to 
sume  ;  and  an  equal  sameness  will  be  found  to  accompany 
^  prolongation,  if  any  other  form  be  originally  given  to  the 

A  method  has  been  suggested  by  Mr.  Wilson,  of  Glasgow,  to 
nder  the  mercury  in  a  thermometer  tube  easily  observable, 
thout  incurring  the  inconveniencies  which  attend  a  laro-e 
re.  1  his  method  is  founded  on  the  property  above  mcntion- 
’  w-, whlch  ls  indeed  common  to  all  ductile  substances* 
r.  Wilson  proposes  to  form  the  tubes  witli  an  elliptical  per- 
ation,  which  when  drawn  out  will  form  a  mere  slit,  the  flat 
e  ot  which  is  to  be  turned  towards  the  observer.  It  does  not 
rear,  however,  that  these  tubes  have  come  into  any  extensive 

rhis  elliptical  bore  is  caused  by  flattening,  in  the  necessary 
free,  and  before  it  is  drawn  out,  the  short  thick  tube  already 
cubed  ;  restoring  then  its  external  cylindric  form  by  coatino- 
ver  with  a  further  portion  of  melted  glass,  and  rolling  it  on 
iron  slab,  mentioned  in  page  137,  in  our  descriptionof  the 
cesses  pursued  in  blowing  flint  glass. 

[’he  apparatus  usually  employed  by  those  who  undertake  this 
uch  of  glass-working  is  extremely  simple.  The  table  is 
stantially  made,  and  has  fixed  at  its  bottom  a  small  double- 
;t  bellows,  worked  with  a  foot-board,  that  the  artist  may- 
self  govern  its  action,  and  at  the  same  time  have  both  his 
as  at  liberty  for  the  other  operations  which  he  has  to  con- 
t.  A  pipe,  proceeding  from  the  bellows,  conducts  the  blast 
•ir  to  the  lamp,  which  is  usually  nothing  but  a  bundle  of 
•se  cotton  thread,  placed  in  a  common  tin  vessel  of  a  horse- 
:  shape,  the  flame  being  fed  with  lumps  of  tallow  heaped  up 
intermixed  with  the  cotton.  A  small  chimney  is  hung  over 
lamp,  and  at  a  short  distance  from  the  flame,  to  carry  off 
;moke,  which  otherwise  would  be  inconvenient  to  the  work- 
•  The  blast  pipe  is  so  placed  and  directed  that  it  throws 
ie  jet  of  flame  from  the  lamp  in  a  direction  contrary  to  that 
pied  by  the  workman,  so  that  all  annoyance  from  this  source 
ually  avoided. 

wo  or  three  very  simple  iron  tools,  such  as  files,  forceps, 
ors,  &c.,  make  up  the  rest  of  the  glass- worker’s  apparatus; 

-  his  materials  are  mostly  confined  to  an  assortment  of 
i  having  various  bores,  and  composed  of  different  thick- 
:s  of  glass.  When  employed  in  making  toys  or  ornaments 
iss,  tubes  of  various  colors  are  provided  by  the  workman : 
are  easily  procurable  at  any  glass-house,  a  good  stock  of 


?0r  If,  beautiful  scientific  application  of  this  principle,  see  Lardner’s  Me- 
s,  Cab.  Cyc.  p.  9.  art.  (12.) 


178  GLASS  MANUFACTURE.  CHAP.  J 

all  kinds  of  tubing  being  generally  kept  by  the  makers.  T 
flame,  when  most  strongly  urged  by  the  blowpipe,  is  about  fi 
inches  long,  having  its  end  of  a  blunt  round  form ;  its  col 
in  the  part  nearest  to  the  wick,  is  of  clear  light  blue,  and 
yond  this  of  a  pale  yellow,  the  blue  portion  having  by  far 
greatest  heating  power. 

In  proceeding  to  work,  care  must  be  taken  to  remove 
moisture  from  the  tubes,  both  within  and  on  the  outside  ;  tl 
must  be  heated  gradually,  to  prevent  their  cracking ;  and 
greater  the  thickness  of  the  glass,  the  more  necessity  there  is 
caution  on  this  head.  Glass  is  so  imperfect  a  conductor  of  he 
that  where  utensils  made  with  it  of  any  considerable  thickn 
have  fire  applied  to  them,  it  is  difficult  to  prevent  an  unequal 
gree  of  expansion,  which  induces  that  corresponding  inequa 
of  pressure  among  the  different  parts  under  which  some  \ 
inevitably  give  way  and  fly  asunder.  It  is  for  this  reason  t 
glasses  intended  for  use  in  chemical  laboratories  can  hardly 
made  too  thin,  or  with  too  great  attention  to  the  equality  of  tl 
substance,  so  that  heat  may  be  quickly  and  uniformly  transmit 
through  the  mass. 

Glass  tubes  should  be  first  heated  by  being  held  in  the  fla 
of  the  lamp,  without  employing  the  blast  of  air ;  they  she 
next  be  brought  to  the  yellow  outer  edge  of  the  flame  wl 
urged  by  the  blowpipe;  and,  lastly,  the  fusion  must  be  complc 
through  bringing  the  glass  by  slow  degrees  within  the  hoti 
part  of  the  flame. 

The  power  of  a  blowpipe,  such  as  is  usually  employed 
these  purposes,  is  sufficient  for  bringing  to  a  white  heat  a  s< 
lump  of  glass  large  enough  to  form  a  bulb  which  will  cont 
three  fluid  ounces ;  a  size  much  larger  than  can  be  required 
purposes  to  which  the  lamp  is  usually  applied. 

It  may  be  well  to  describe  briefly  one  or  two  operations,  s 
as  are  usually  effected  by  means  of  the  lamp  and  blovvpi 
from  which  will  be  made  apparent  the  great  facility  wherev 
this  seemingly  refractory  substance  can  be  moulded,  throi 
the  agency  of  heat,  according  to  the  will  of  the  workman. 

If  it  be  wished  to  seal  a  tube  hermetically,  that  is,  to  clos 
effectually  at  the  end  by  causing  the  intimate  union  of  its  j 
tides,  it  will  suffice  that  the  part  be  held  during  a  short  t 
in  the  flame,  turning  the  tube  round  with  the  fingers  so  a 
occasion  an  equal  action  upon  every  part :  by  this  means 
end  will  presently  be  so  far  softened,  or  partially  fused,  that 
particles  will  fall  in  and  run  together;  thus  effectually  do4 
the  orifice,  and  producing  the  appearance  of  a  small  butto 
the  extremity.  This  operation  may  be  hastened,  if,  when 
glass  is  rendered  soft  by  heat,  and  before  any  fusion  has  ensi 


iAP.  IX.  BINDING  TUBES.  179 

e  parts  are  brought  into  contact  towards  their  common  centre 
'  means  of  a  stout  iron  needle.  In  some  cases,  and  partieular- 
wheu  the  tube  is  of  any  considerable  substance,  the  button 
us  formed  on  the  end  would  be  inconveniently  large,  and 
ight  besides  either  fly  in  cooling-,  or  be  accidentally  broken. 
!iis  can  be  remedied  by  lessening,  in  the  following  manner, 
e  quantity  of  glass  whereof  it  is  composed. 

The  end  being  softened  in  the  flame  of  the  lamp,  and  another 
3ce  of  tube  of  the  same  size  having  been  equally  acted  upon, 
e  two  ends  are  to  be  brought  together,  and  may,  by  a  very 
tie  management,  be  firmly  united.  If  then  the  tube  which  is 
be  sealed  is  softened  a  little  higher  up  than  the  point  of 
ion,  and  the  two  tubes  are  pulled  gently  in  opposite  directions 
itil  they  separate,  that  which  is  heated  will  be  drawn  out  with 
liminished  substance,  and  may  be  easily  sealed  in  the  part 
it  is  required,  the  joined  ends  and  a  portion  of  the  sealed  tube 
maining  attached  to  the  waste  piece. 

In  making  some  kinds  of  thermometers,  and  for  various  pur¬ 
ses  connected  with  experimental  chemistry,  it  is  often  requir- 
to  bend  tubes  of  glass :  when  these  are  of  small  bore,  and 
eir  substance  is  tolerably  thick,  it  is  only  requisite  to  hold  the 
be  in  the  weaker  part  of  the  flame,  in  order  to  soften  it 
rough  about  one  or  two  inches  of  its  length,  when  it  may  be 
iwly  and  gently  brought  to  the  shape  required. 

Something  more  than  this  is  needed  if  the  tube  be  wide  and 
substance  thin.  In  order  to  preserve  in  sucli  case  the  particu- 
•  form  of  the  bore,  and  to  prevent  its  being  much  straightened, 
perhaps  closed  at  the  bend,  as  it  most  probably  would  be  if  no 
ecaution  were  taken  against  it,  one  end  of  the  tube  should  be 
rmetically  sealed  ;  and  during  the  time  the  workman  employs 
nself  in  bending  it  at  the  required  part,  he  should  also  blow 
sadily  but  very  gently  into  the  open  end.  The  pressure  of 
!  breath  employed  in  this  manner,  will  keep  the  softened 
rt  of  the  tube  distended  in  the  proper  degree,  so  that  it  can- 
t  collapse  during  the  bending,  and  the  perforation  will  be 
tintained  in  its  original  form.  The  closed  end  of  the  tube 
ly  be  readily  cut  off  by  first  scratching  with  a  file  and  then 
jaking  it  suddenly ;  an  operation  which,  with  a  very  little 
•e,  may  be  performed  without  risk  of  dividing  the  tube  in  any 
ler  part  of  its  length. 

Two  tubes  may  be  joined  together  with  tolerable  accuracy 
heating  their  ends  in  the  flame,  and  then  bringing  them 
o  contact ;  turning  them  round  in  opposite  directions  with  a 
ewing  motion,  in  order  to  complete  their  junction.  If  it  be 
sired  to  remove  the  thickened  ring  of  glass  which  will  thus 
produced,  one  end  of  the  tube  must  then  be  previously  seal- 


180 


GLASS  MANUFACTURE. 


CHAP.  IX 


ed  ;  and  when  the  union  has  been  fully  completed  in  the  wa 
described,  and  while  the  glass  is  yet  soft,  the  workman  mm 
blow  into  the  open  end,  and  gently  pull  the  tube  at  the  point  o 
junction,  until  the  ring  disappears,  and  the  whole  tube  become 
equally  cylindrical. 

In  forming  hollow  bulbs  at  the  end  of  tubes,  such,  for  ir 
stance,  as  are  required  in  making  thermometers,  the  followin 
process  must  be  used : — The  end  whereat  the  bulb  is  to  be  forn: 
ed  must  be  sealed ;  and  in  order  to  collect  at  this  extremity  th 
needful  quantity  of  glass,  it  must  be  pressed  while  yet  quite  he 
upon  some  hard  surface,  by  which  means  that  part  is  somewha 
shortened  and  consolidated  into  a  lump.  This  must  then  b 
held  in  the  most  intense  flame  of  the  blowpipe  until  it  is  quit 
white  hot ;  being  then  removed,  and  the  breath  applied  model 
ately  and  steadily  to  the  open  end,  and  keeping  the  tube  in  th 
meanwhile  with  the  heated  end  hanging  downwards,  th 
lump  will  be  enlarged  into  a  spherical  bulb,  the  diameter,  an' 
consequently  the  substance,  of  which  can  be  regulated  accord 
ing  to  the  pleasure  of  the  workman. 

It  has  been  already  mentioned  that  glass  may  be  spun  int 
very  long  and  minute  threads,  with  great  velocity,  when  th' 
mass  from  which  it  is  drawn  has  been  previously  heated.  Fo 
this  operation  the  use  of  the  blowpipe  is  required,  and  the  man 
ner  of  its  performance  is  very  simple. 

The  lump  of  glass  being  sufficiently  softened  by  the  flame 
another  piece  of  glass  is  applied  to  it,  when  the  two,  coherin' 
together,  and  being  then  drawn  apart,  are  seen  to  be  connects 
by  minute  filaments.  A  fine  thread  being  thus  obtained,  its  en< 
is  applied  to  a  wheel  or  reel,  and  the  heat  of  the  glass  bein' 
maintained,  while  the  wheel  is  turned  with  considerable  velo 
city,  a  thread  may  be  drawn  continuously  out  as  long  as  tin 
workman  pleases,  or  until  the  store  of  glass  is  wholly  expended 

The  thread  thus  made  is  extremely  flexible  and  delicate!) 
fine.  Its  firmness  depends  in  a  great  measure  upon  the  hea 
whereat  the  glass  is  maintained,  and  upon  the  velocity  where 
with  the  wheel  is  turned :  the  greater  these  are,  the  firmer  wil 
be  the  thread. 

Glass  is  only  treated  in  this  manner  in  order  to  afford  a  pleas' 
ing  exemplification  of  some  of  its  properties,  or  for  purposes  of 
ornament.  When  it  is  desired  to  produce  colored  threads,  the 
material  employed  should  be  embued  with  a  very  deep  tint,  as 
when  drawn  out  in  such  minute  filaments,  it  would  otherwise 
appear  nearly  colorless. 

The  preparation  of  watch-glasses  involves  a  series  of  simple 
but  interesting  processes.  Only  a  part  of  these  is  performed  al 


CIIAP.  IX. 


WATCH-GLASSES. 


181 


the  glass-house ;  the  remainder  being  the  objects  of  a  separate, 
and,  when  viewed  with  reference  to  its  extent,  by  no  means 
unimportant  branch  of  trade  and  manufacture. 

All  that  is  effected  by  the  glass-blower  is  the  production  of 
regular  hollow  spheres,  each  being  eight  inches  in  diameter, 
and  weighing  twelve  ounces. 

It  is  a  circumstance,  perhaps,  not  the  least  deserving  of  notice, 
in  detailing  the  operations  of  the  glass-house,  that  the  men  em¬ 
ployed  to  gather  glass  from  the  pots  for  this  and  similar  pur¬ 
poses,  upon  the  end  of  the  hollow  rods,  attain  through  constant 
practice  so  much  proficiency  as  to  bring  away  with  the  great¬ 
est  accuracy  exactly  the  quantity  that  is  needed  for  the  forma¬ 
tion  of  the  required  object.  To  such  a  degree  is  this  correct¬ 
ness  ca  rried,  that,  on  weighing  many  dozens  of  spheres  such  as 
have  just  been  described,  not  one  has  been  found  that  varies 
half  an  ounce  from  the  proper  weight. 

The  blowing  of  these  hollow  globes  is  performed  with  great 
celerity.  Owing  to  the  circumstance  that  the  glass  of  which 
they  are  composed  is  exceedingly  thin,  so  that  their  cooling, 
although  rapid,  is  also  effected  with  considerable  regularity 
through  their  substance ;  and  because  in  the  further  progress 
towards  their  ultimate  form  they  are  again  to  be  softened  by 
heat,  these  globes  are  delivered  to  the  watch-glass  maker  as 
soon  as  they  are  blown,  and  without  passing  through  the 
annealing  oven. 

The  first  operation  performed  by  the  last-mentioned  artist  is 
to  divide  each  sphere  into  the  largest  possible  number  of  sec¬ 
tions  of  the  requisite  size ;  it  being  manifest  that  any  errors 
committed  at  this  stage  of  the  proceeding  would,  by  wasting 
his  material,  place  the  manufacturer  at  a  disadvantage. 

In  proceeding  to  effect  this  division,  the  workman  seats  him¬ 
self  ;  and  taking  the  globe  in  his  lap,  with  a  piece  of  heated 
wire  or  tobacco-pipe,  (which  last  is  perhaps  chosen  preferably, 
because  it  longer  retains  a  sufficient  degree  of  heat,)  he  traces 
a  line  upon  the  globe,  and  quickly  thereafter  wetting  the  line 
thus  traced,  the  glass  will  crack  and  divide  along  the  line  with 
the  most  admirable  precision.  The  sections  thus  obtained  will 
necessarily  have  many  angular  irregularities :  these  are  dexter¬ 
ously  clipped  away  by  means  of  scissors. 

The  segments  into  which  the  individual  pieces  have  now 
been  cut,  will  be  wanting  in  the  requisite  degree  of  convexity. 
Before  this  can  be  imparted  to  them,  they  must  have  their  brit¬ 
tleness  removed,  and  be  considerably  softened  by  heat.  When 
this  has  been  effected,  taking  an  appropriate  instrument  in  each 
hand,  and  using  them  much  in  the  same  manner  as  the  dairy¬ 
maid  employs  her  wooden  spoons  in  raising  a  pat  of  butter, 

Q 


182  GLASS  MANUFACTURE.  CHAP.  IX. 

the  workman  presses  the  edges  of  the  glass  regularly  in  to¬ 
wards  the  centre,  which  is  by  this  means  made  to  rise  in  a  cor¬ 
responding  proportion.  The  edges  are  then  ground  evenly  off, 
and  the  watch-glass  is  ready  for  sale. 

Lunette  glasses  are  differently  made.  These  are  not  seg¬ 
ments  of  spheres,  but  have  their  edges  abruptly  raised,  and 
their  interior  areas  or  faces  flattened.  In  forming  these  lu¬ 
nettes,  a  much  smaller  quantity  of  glass  is  gathered  from  the 
pot  than  is  required  in  blowing  globes  for  ordinary  watch- 
glasses.  A  hollow  pear-shaped  figure  is  then  blown,  having 
the  larger  end,  which  is  farthest  from  the  extremity  of  the  rod, 
of  the  size  required  for  a  watch-glass,  and  the  requisite  flat¬ 
ness  is  occasioned  by  pressing  this  end,  while  soft,  upon  any 
smooth  level  surface. 

These  glasses  are  necessarily  much  higher  in  price  than 
those  more  commonly  used  for  watches ;  both  because  they  are 
made  to  contain  a  greater  weight  of  glass,  and  because,  only 
one  form  being  cut  from  each  hollow  pear-shaped  figure,  the 
labor  expended  in  the  manufacture  is  proportionally  greater. 

A  very  considerable  manufacture  of  glass  for  the  formation 
of  beads  is  carried  on  at  a  place  called  Murano,  situated  near 
the  city  of  Venice.  There  is  nothing  peculiar  in  the  composi¬ 
tion  of  the  glass  made  use  of  for  this  purpose,  nor  in  the  meth¬ 
ods  employed  for  its  preparation ;  and  although  the  manufactu¬ 
rers  affect  great  secrecy  as  to  the  coloring  substances  which 
they  mix  with  the  glass,  it  is  not  likely  that  they  possess  any 
real  advantage  over  others  in  this  respect,  or  that  they  have 
made  any  useful  discovery  of  materials  different  from  those 
commonly  employed  in  coloring  glass. 

When  upon  inspection  the  colored  glass  is  found  to  be  in  a 
fit  state  for  working,  the  necessary  quantity  is  gathered  in  the 
usual  manner  upon  the  rod,  and  is  blown  into  a  hollow  form. 
A  second  workman  then  provides  himself  with  an  appropriate 
instrument,  with  which  he  takes  hold  of  the  glass  at  the  end 
which  is  farthest  from  the  extremity  of  the  rod,  and  the  two 
men  running  thereupon  expeditiously  in  exactly  opposite  direc¬ 
tions,  the  glass  is  drawn  out  into  a  pipe  or  tube,  in  the  manner 
of  those  used  for  constructing  thermometers,  the  thickness  of 
which  depends  upon  the  distance  by  which  the  men  separate 
themselves.  Whatever  this  thickness  may  be,  the  perforation 
of  the  tube  is  preserved,  and  bears  the  same  proportion  rela¬ 
tively  to  the  substance  of  the  glass  as  was  originally  given  to 
it  by  the  blower.  In  these  particulars  the  workmen  of  course 
govern  themselves  according  to  the  size  and  description  of  the 
beads  which  are  to  be  made.  The  glass-house  at  Murano  is 


CHAP.  IX. 


GLASS  BEADS. 


183 


provided  with  a  kind  of  gallery  150  feet  in  length,  and  which 
much  resembles  a  rope- walk,  wherein  the  tubes  are  drawn  out 
in  the  manner  here  described. 

Tubes  striped  witli  different  colors  are  made  by  gathering 
from  two  or  more  pots  lumps  of  different  colored  glass,  which 
are  united  by  twisting  them  together  before  they  are  drawn 
out  to  the  requisite  length. 

As  soon  as  they  are  sufficiently  cool  for  the  purpose,  the 
tubes  are  divided  into  equal  lengths,  sorted  according  to  their 
colors  and  sizes,  packed  in  chests,  and  then  dispatched  to  the 
city  of  Venice,  within  which  the  actual  manufacture  of  the 
beads  is  conducted. 

When  they  arrive  at  the  bead  manufactory,  the  tubes  are 
again  very  carefully  inspected,  and  sorted  according  to  their 
different  diameters,  preparatory  to  their  being  cut  into  pieces 
sufficiently  small  for  making  beads. 

For  performing  this  latter  operation,  a  sharp  iron  instrument 
is  provided,  shaped  like  a  chisel,  and  securely  fixed  in  a  block 
of  wood.  Placing  the  glass  tube  upon  the  edge  of  this  tool 
at  the  part  to  be  separated ;  the  workman  then,  with  another 
sharp  instrument  in  his  hand,  cuts,  or  rather  chips,  the  pipe 
into  pieces  of  the  requisite  size;  the  skill  of  the  man  being 
shown  by  the  uniformity  of  size  preserved  between  the  differ¬ 
ent  fragments. 

The  minute  pieces  thus  obtained  are  in  the  next  process 
thrown  into  a  bowl  containing  a  mixture  of  sand  and  wood- 
ashes,  in  which  they  are  continually  stirred  about  until  the 
perforations  in  the  pieces  are  all  filled  by  the  sand  and  ashes. 
This  provision  is  indispensable,  in  order  to  prevent  the  sides 
from  falling  together  when  softened  by  heat  in  the  next  opera¬ 
tion. 

A  metallic  vessel  with  a  long  handle  is  then  provided, 
wherein  the'  pieces  of  glass  are  placed,  together  with  a  further 
quantity  of  wood-ashes  and  sand ;  and  the  whole  being  subject¬ 
ed  to  heat  over  a  charcoal  fire,  are  continually  stirred  with  a 
'hatchet-shaped  spatula.  By  this  simple  means  the  beads  ac¬ 
quire  their  globular  form. 

When  this  has  been  imparted,  and  the  beads  are  again  cool, 
they  are  agitated  in  sieves,  in  order  to  separate  the  sand  and 
ashes ;  this  done,  thev  are  transferred  to  other  sieves  of  differ¬ 
ent  degrees  of  fineness,  in  order  to  divide  the  beads  according 
to  their  various  sizes.  Those  of  each  size  are  then,  after  being 
strung  by  children  upon  separate  threads,  made  up  into  bun¬ 
dles,  and  packed  in  casks  for  exportation. 

In  this  manner,  not  fewer  than  sixty  different  kinds  of  glass 
beads  are  prepared  in  vast  quantities.  The  principal  trade  in 


GLASS  MANUFACTURE. 


CHAP.  IX, 


184 

these  is  carried  on  with  Spain  and  the  coast  of  Africa;  but 
some  portions  find  their  way  to  nearly  all  parts  of  the  world. 

Another  and  a  more  costly  description  of  glass  beads,  made 
in  imitation  of  pearls,  has  long  been  produced  in  France.  Al¬ 
though  the  name  of  the  inventor  of  these  ornaments  has  been 
faithfully  preserved,  the  period  of  their  invention  is  not  pre¬ 
cisely  known.  Reaumur,  on  whose  assertions  the  greatest  re¬ 
liance  may  generally  be  placed,  states  this  to  have  occurred  in 
1856.  An  anecdote  related  by  Beckmann*  of  a  cheat  success¬ 
fully  played  off  upon  a  lady  by  a  French  nobleman,  leads  to  the 
conclusion  that  thirty  years  later  than  the  period  here  mention¬ 
ed,  these  mock  pearls  were  far  from  being  generally  introduced 
or  even  known. 

The  manner  of  their  invention  was  this : — M.  Jaquin  having 
observed  that  upon  washing  a  small  fish,  the  Cyprinus  albur- 
nus,  or  bleak,  the  water  contained  numerous  fine  particles, 
having  the  color  of  silver,  and  a  pearly  lustre,  he  suffered  the 
water  to  stand  for  some  time,  and,  collecting  the  sediment, 
covered  with  it  some  beads  made  of  plaster  of  Paris,  the  fa¬ 
vorable  appearance  of  which  induced  him  to  manufacture  more 
of  the  same  kind  for  sale.  These  were  at  first  eagerly  adopt¬ 
ed  ;  but  the  ladies  soon  finding  that  when  they  were  exposed 
to  heat,  the  lustrous  coating  transferred  itself  from  the  beads 
to  their  skin,  they  were  as  quickly  discarded. 

The  next  attempt  of  M.  Jaquin  was  more  successful.  He 
procured  some  glass  tubes  of  a  quality  easily  fusible,  and,  by 
means  of  a  blowpipe,  converted  these  into  numerous  hollow 
globules.  He  then  proceeded  to  line  the  interior  surface  of 
these  with  the  powdered  fish-scales,  which  he  called  essence 
of  pearl,  or  essence  <T  Orient.  This  was  rendered  adhesive  by 
being  mixed  with  a  solution  of  isinglass,  when  it  was  intro¬ 
duced  in  a  heated  state  inside  the  globules,  and  spread  over  the 
whole  interior  surface,  by  shaking  the  beads  which,  for  that 
purpose,  were  placed  in  a  bowl  upon  the  table.  These  hollow 
beads  being  blown  exceedingly  thin,  in  order  to  produce  a  bet¬ 
ter  effect,  were  consequently  very  tender.  To  remedy  this 
evil,  as  soon  as  the  pearly  varnish  was  sufficiently  dry,  they 
were  filled  with  white  wax,  and  being  then  bored  through  with 
a  needle,  were  threaded  for  sale. 

An  expert  workman  can  blow  from  five  to  six  thousand  small 
glass  globules  in  a  day ;  but,  as  some  attention  is  called  for  in 
regard  to  the  shape  and  appearance  of  these  beads,  the  produce 
of  a  man’s  daily  labor  will  not  much  exceed  one  fourth  of  that 
quantity.  The  closer  to  counterfeit  nature  in  their  manufacture, 


*  Hist,  of  Inventions,  vol.  ii.  art.  Artificial  Pearls. 


MOCK  PEARLS. 


CHAP.  IX. 

1 


185 


these  beads  are  sometimes  purposely  made  with  blemishes,  and 
of  somewhat  irregular  forms.  Some  are  made  pear-shaped; 
others  are  elongated  like  olives ;  and  others  again  are  flattened 
on  one  side,  in  imitation  of  natural  pearls,  which  are  set  in  a 
manner  to  show  only  one  side. 

The  fish  whose  scales  are  put  to  this  use  are  about  four 
inches  in  length.  They  are  found  in  great  abundance  in  some 
rivers ;  and,  being  exceedingly  voracious,  suffer  themselves  to 
be  taken  without  difficulty.  The  scales  furnished  by  250  of 
these  fish  will  not  weigh  more  than  an  ounce,  and  this  will  not 
yield  more  than  a  fourth  of  that  quantity  of  the  pearly  powder 
applicable  to  the  preparation  of  beads ;  so  that  16,000  fish  are  re¬ 
quired  in  order  to  obtain  only  one  pound  of  the  essence  of  pearl. 

Up  to  a  recent  period,  the  heirs  of  Jaquin,  the  first  inventor, 
carried  on  a  considerable  manufactory  of  these  mock  pearls  in 
Paris.  The  fish  are  tolerably  abundant  in  the  river  Seine ;  but 
their  scales  are  conveyed  from  distant  parts  in  much  larger 
quantities  than  can  be  procured  on  the  spot,  for  which  purpose 
they  are  preserved  in  volatile  alkali. 


The  dial-plates  of  clocks  and  watches  are  made  of  opaque 
white  glass,  which  has  acquired  the  name  of  enamel.  The  pe¬ 
culiarly  delicate  appearance  of  these,  as  well  as  their  opaque¬ 
ness,  result  from  the  presence  of  oxide  of  tin. 

These  plates,  which  are  not  of  greater  diameter  than  twelve 
inches,  are  made  in  one  piece ;  but  any  which  are  required  to 
be  larger  than  this,  must  be  formed  in  separate  segments,  and 
afterwards  joined  together. 

In  the  preparation  of  dial-plates,  the  first  process  is  that  of 
hammering  a  thin  plate  of  copper  of  the  requisite  size  upon  a 
slightly  concave  anvil  constructed  of  hard  wood ;  for  which 
operation  a  convex  hammer  is  employed,  and  in  this  manner 
the  proper  state  of  convexity  is  imparted  to  the  plate,  without 
impairing  in  any  degree  the  smoothness  of  its  surface. 

The  centre  hole  for  the  hour  and  minute  hands,  as  well  as 
that  whereby  the  key  must  be  introduced  for  the  purpose  of 
winding  up  the  clock  or  watch,  together  with  other  smaller 
holes,  for  the  screws  by  which  the  dial  is  to  be  attached  to  the 
works,  are  all  made  by  passing  tools  of  appropriate  forms  and 
sizes  through  the  copper,  from  the  concave  side,  in  such  a  man¬ 
ner  that  the  metal  displaced  in  the  act  may  form  ridges  round 
the  holes  on  the  convex  side,  and  be  instrumental  in  retaining 
the  enamel  to  the  requisite  thickness  upon  the  surface,  when 
in  its  state  of  fusion.  For  this  same  purpose,  the  outside  edge 
of  the  plate  is  hammered  up  all  round,  so  as  to  form  a  ridge  of 
the  requisite  depth ;  and  provision  must  be  made  for  this  rim 

Q  2 


18G 


GLASS  MANUFACTURE. 


CHAP.  IX. 


in  the  size  originally  given  to  the  copper.  The  metallic  plate 
thus  formed  is  thoroughly  cleansed  by  being  immersed  in  a 
weak  dilution  of  nitric  acid,  after  which  it  is  dipped  in  pure 
water,  and  rubbed  smartly  over  with  a  brush  formed  of  brass 
wires. 

The  white  enamel  is  then  broken  in  a  hardened  steel  mor¬ 
tar,  until  it  is  reduced  to  fragments  about  the  size  of  fine 
sand  ;  and  the  whole  should  be  brought  as  nearly  as  possible  to 
the  same  state  as  regards  the  size  of  the  particles.  The  pounded 
glass  is  then  washed  in  very  clear  water,  and  the  heavier  parts 
having  subsided,  the  remaining  milky-looking  liquid  is  poured 
off  and  left  to  settle  in  a  separate  vessel.  This  operation  is 
several  times  repeated ;  so  that  the  powder  may  be  divided  into 
separate  portions,  having  different  degrees  of  fineness. 

The  enamel  being  thus  sorted  and  well  washed,  the  separate 
portions  are  placed  in  glass  vessels,  and  nitric  acid  is  poured 
over,  so  as  completely  to  cover  the  powders.  The  acid  must 
be  left  on  the  enamel  during  the  space  of  twelve  hours,  the 
whole  being  occasionally  stirred  with  a  glass  spatula,  in  order 
to  dissolve  away  any  metallic  particles  which  may  have  been 
abraded  from  the  steel  mortar,  and  which  would  greatly  impair 
the  whiteness  of  the  enamel  when  subsequently  applied  on  the 
face  of  the  plate.  The  acid  is  then  poured  off,  and  the  enamel 
washed  in  successive  waters,  until  it  no  longer  contains  any 
acidity ;  after  which,  it  is  again  covered  with  pure  water,  and 
in  this  state  it  must  remain  until  used,  that  its  perfect  white¬ 
ness  and  purity  may  be  preserved. 

It  is  necessary  to  operate  upon  both  sides  of  the  plate,  lest 
the  heat  of  the  enamel,  when  in  a  state  of  fusion  on  the  con¬ 
vex  side,  should  alter  the  curvature  of  the  copper,  and  deform 
its  shape. 

The  enamel,  when  prepared  in  the  manner  described,  is  first 
applied  to  the  concave  or  under  face ;  in  which  process  the 
artist  spreads  over  it  with  a  spatula,  as  thin  and  as  evenly  as 
possible,  a  portion  of  the  finer  settlings.  A  tool  which  had  pre¬ 
viously  been  i  nserted  in  the  centre  hole  is  then  withdrawn,  and 
its  place  sup] (lied  with  a  rag  of  clean  linen,  which  absorbs  all 
the  superfluous  water  from  the  enamel,  bringing  it  to  such  a 
state  of  consistency,  that  this,  which  is  called  the  counter-en¬ 
amelling,  will  adhere  sufficiently  to  the  copper  when  the  posi¬ 
tion  of  the  plate  shall  be  reversed.  In  then  proceeding  to  op¬ 
erate  upon  the  convex  surface,  the  plate  must  be  turned  over, 
a  tool  being  again  placed  in  the  centre  hole,  and  a  layer  of  the 
coarser  part  of  the  pounded  glass  thereafter  applied  with  every 
possible  care  as  to  the  evenness  of  its  distribution.  It  is  par¬ 
ticularly  requisite  to  cover  well  the  edges  of  the  dial-plate,  as 


CHAP.  IX.  DIAL  PLATES.  JQ7 

well  as  those  of  the  different  holes,  lest  the  heat  should  after¬ 
wards  act  too  powerfully  upon  the  metal.  To  draw  off  the  su¬ 
perfluous  moisture  from  this  layer  of  enamel,  a  fine  linen  cloth 
is  applied  round  the  entire  edge,  which,  in  this  altered  position 
of  the  dial,  is  now  its  lowest  part,  and  has  in  that  respect  taken 
1  the  place  of  the  centre  hole  in  the  counter-enamelling  process 
hist  mentioned.  In  order  that  the  particles  mav  arrano-e  them¬ 
selves  properly  and  closely  together,  the  tool  still  remaining  in 
the  centre  hole  is  then  subjected  to  two  or  three  slight  concus¬ 
sions,  and  much  of  the  beautiful  appearance  of  the  finished 
dial-plate  depends  upon  the  neatness  with  which  this  operation 
is  performed.  If  the  enamel  is  evenly  spread  and  well  packed 
together,  no  hollows  will  be  left  below  the  surface  when  it  has 
ibeen  melted,  and  the  requisite  degree  of  smoothness  will  be  at¬ 
tained.  To  dissipate  any  moisture  which  may  now  be  retained 
iy  the  enamel,  the  plate  is  dried  on  a  sheet  of  iron  over  a 
chafing-dish. 

The  dial-plate,  thus  prepared,  is  introduced  cautiously  and 
by  degrees  under  a  muffle  placed  in  a  furnace,  it  beino-  neces¬ 
sary  to  heat  it  gradually:  in  this  situation  it  must  remain  until 
it  is  perceived  that  the  enamel  begins  to  melt ;  the  sheet  of 
;ron  on  which  the  dial  is  placed  should  then  be  turned  o-ently 
round,  in  order  that  every  part  may  be  equally  exposed *to  the 
leat  of  the  muffle.  So  soon  as  the  enamel  is  seen  to  be  per¬ 
fectly  melted  over  the  whole  surface,  the  plate  must  be  with¬ 
drawn  with  as  much  caution  and  deliberateness  as  was  used 
lpon  its  introduction ;  and,  in  order  to  prevent  the  cracking1 
md  scaling  off  to  which  the  glass  would  otherwise  be  liable 
i  he  plate  must  remain  for  some  time  cooling  very  gradually  at 
he  mouth  of  the  muffle.  The  necessity  for  this  delay  in  the 
irocess  arises  from  the  same  physical  law  which  obliges  the 
|  Manufacturer  to  have  recourse  in  larger  operations  to  the 
I  annealing  oven. 

When  this  first  firing  has  been  completed,  the  plate  must  be 
leaned,- as  before,  with  a  very  weak  dilution  of  nitric  acid  1 
nd  a  layer  of  the  finer  settlings  of  the  enamel  is  to  be  spread,’ 

I  a  the  manner  already  described,  over  the  convex  side  It  is 
ot  necessary  to  apply  any  further  coating  to  the  inner  or  con- 
:  ave  surface,  unless  upon  examination  any  part  of  the  former 
iyer  shall  appear  defective  ;  in  which  case  such  part  must  be 
mde  good  with  a  further  portion  of  the  same  division  of  the 
namel  as  was  used  before. 

The  same  precautions  that  were  observed  in  the  first  firino- 
>r  placing  the  dial-plate  within,  and  for  removing  it  from  the 
iuffle,  must  be  repeated  now  ;  and  must  equally  be  practised 
ben  a  third  layer,  which  must  be  of  the  finest  and  whitest 


188  GLASS  MANUFACTURE.  CHAP.  IX. 

portion  of  the  enamel,  is  subsequently  spread  over  the  convex 
side.  When  this  third  layer  has  in  its  turn  been  fused  and 
gradually  cooled,  the  dial-plate  is  complete,  with  the  exception 
of  the  figures  or  lettering,  which  must  he  placed  upon  the  con¬ 
vex  side  to  mark  the  divisions  of  the  hours  and  minutes,  and 
which  are  thus  applied  : — 

A  black  enamel,  which  is  so  composed  that  it  will  fuse  at  a 
lower  degree  of  heat  than  the  white  opaque  glass  already  em¬ 
ployed,  is  to  be  ground  exceedingly  fine  in  an  agate  mortar 
with  a  pestle  of  the  same  substance,  and  in  combination  with 
oil  of  lavender ;  which,  as  it  would  of  itself  be  too  thick,  must 
have  its  consistence  reduced  by  the  addition  of  oil  of  turpentine. 
To  such  an  exceeding  degree  of  fineness  is  it  considered  ne¬ 
cessary  to  reduce  this  black  enamel  for  the  purpose,  that  the 
labor  of  half  a  day  is  usually  employed  in  thus  grinding  a  drachm 
weight.  A  further  quantity  of  the  mixed  essential  oils  must 
afterwards  be  added,  that  the  enamel  may  be  sufficiently  thin 
to  flow  readily  from  the  pencil. 

The  dial-plate  is  then  placed  upon  some  level  surface,  and 
by  means  of  a  pair  of  compasses,  having  one  of  the  legs  blunt 
at  the  end  and  rounded,  so  that  it  will  freely  turn  in  the  centre 
hole  where  it  is  placed,  and  the  other  leg  provided  with  a  black- 
lead  pencil,  two  circular  lines  are  slightly  traced  at  unequal 
distances  from  the  centre,  between  which  the  numerals  are  to 
be  inserted.  The  exact  position  of  these  is  determined  by 
means  of  a  sector  furnished  with  a  movable  limb ;  and  the  dif¬ 
ferent  figures  being  drawn  with  a  camel’s  hair  pencil  charged 
with  the  prepared  black  enamel,  this  is  left  to  become  pefectly 
dry  in  the  air ;  and  its  fusion  having  afterwards  been  effected 
in  the  muffle,  the  dial-plate  is  completed,  and  in  a  fit  state  to 
be  placed  in  the  hands  of  the  clockmaker. 


CHAP.  X. 


FORMATION  OF  LENSES. 


189 


CHAP.  X. 

ON  THE  FORMATION  OF  LENSES. 

Preparations  of  the  necessary  Tools. — Choice  of  Glass. — Grinding. — Polish¬ 
ing. — Curdled  Lenses. — Means  used  for  avoiding  this  Defect. 

In  grinding  glass  for  spectacles,  or  preparing  them  as  lenses 
for  optical  instruments,  the  first  thing  to  be  attended  to  is  to  de¬ 
termine  the  proper  focal  distance  of  the  glass.  Taking  then  a 
pair  of  compasses,  which,  on  the  supposition  that  the  glass  is 
intended  to  be  convex  or  concave  on  both  sides,  must  be  opened 
to  the  full  focal  distance ;  two  arches  or  segments  of  circles, 
each  extended  somewhat  beyond  the  breadth  which  it  is  in¬ 
tended  to  give  to  the  glass,  must  be  described  upon  a  piece  of 
sheet  copper,  which  must  then  be  filed  away  from  the  out¬ 
side  of  one  and  from  the  inside  of  the  other  arch.  By  this 
means  two  gauges  are  formed,  the  one  convex  and  the  other 
concave,  and  each  perfectly  answering  to  the  other. 

If  it  is  intended  that  the  glass  shall  be  what  the  opticians  call 
plano-convex  or  plano-concave,  that  is,  having  one  of  its  sides 
flat,  while  the  other  has  received  the  requisite  curvature,  the 
compasses  wherewith  the  arches  are  described  should  be  opened 
to  only  one  half  the  focal  distance. 

Two  circular  plates  of  brass,  about  one-tenth  of  an  inch  in 
thickness,  and  each  being  of  a  little  larger  diameter  than  the 
intended  lenses,  are  then  securely  soldered  upon  a  cylindrical 
piece  of  lead  of  an  equal  diameter  with  the  brass  discs,  and  one 
inch  in  thickness ;  these,  which  are  called  tools,  are  then  fixed 
in  the  lathe,  and  turned  so  as  to  correspond  with  the  copper 
gauges,  the  surface  of  one  being  made  convex,  and  of  the  other 
2oncave. 

The  two  brass  discs  are  then  to  be  ground  together  with 
emery,  or  with  pounded  Turkey-stone,  until  their  surfaces  ex¬ 
actly  coincide  in  every  point. 

If  the  focal  distance  is  very  short,  so  that  the  convexity  and 
■oncavity  require  to  be  very  considerable,  the  brass  discs  should 
he  hammered  as  nearly  as  possible  to  their  intended  form  be- 
bre  they  are  soldered  to  the  leaden  cylinders,  and  turned ; 
therwise  either  the  thickness  of  the  brasses  would  require  to 
>e  inconveniently  increased,  or  the  more  considerable  portion  of 
heir  substance,  which  must  in  such  case  be  cut  away,  would 
ccasion  the  discs  to  be  too  thin  and  yielding. 

The  glass  of  which  a  lens  is  composed  is  chosen  with  refer- 
nce  to  the  purpose  to  which  it  is  to  be  applied,  and  according 
jits  refraetive  and  dispersive  powers:  its  selection  must  be 


GLASS  MANUFACTURE. 


CHAP.  X. 


190 


left  to  the  discretion  of  the  optician.  Its  two  surfaces  should 
originally  be  perfectly  parallel.  Being  cut  or  clipped  into  a 
circular  form  by  means  of  scissors  or  pincers,  the  edge  must  be 
smoothed  on  a  common  grindstone,  and  the  glass  fixed  by  seat¬ 
ing  one  of  its  surfaces  in  softened  pitch  on  the  flat  end  of  a  solid, 
cylindrical,  wooden  handle  of  smaller  diameter  than  the  glass. 
The  centre  of  the  axis  of  this  handle  must  coincide  exactly  with 
the  centre  of  the  glass. 

If,  to  suit  a  short  focal  distance,  the  curvature  of  the  lens  re¬ 
quires  to  be  great,  it  will  simplify  the  labor  of  the  artist,  if,  pre¬ 
viously  to  its  being  thus  fitted  to  its  handle,  the  glass  is  reduced 
upon  the  grindstone  as  nearly  as  possible  to  the  shape  of  the 
gauge.  Some  judgment  is,  however,  necessary  in  this  process, 
lest  the  abrasion  should  be  carried  too  far,  even  in  any  one  mi¬ 
nute  point,  which  would  render  the  glass  wholly  unserviceable. 

The  convex  form  is  that  which  is  most  commonly  given  to 
lenses;  and  in  describing  the  process  for  effecting  this,  the 
mode  of  producing  concave  glasses  will  equally  be  understood ; 
the  only  difference  between  the  two  methods  being  this, — that 
in  the  first  operation,  the  concave  tool  and  gauge  are  brought 
into  use  ;  while  for  the  other,  those  having  a  convex  form  are 
employed. 

The  whole  being  thus  prepared,  the  concave  tool  is  fixed 
firmly  on  the  working  bench;  and  having  some  fine  emery 
sprinkled  on  its  surface,  the  glass  is  worked  upon  it  with  circu¬ 
lar  and  cross  strokes  alternately ;  the  artist  being  careful  that 
the  centre  of  the  glass  shall  never  pass  beyond  the  edge  of  the 
tool. 

When  by  these  means  the  glass  has  been  so  far  ground  that 
its  surface  coincides  with  that  of  the  tool  at  every  point,  the 
emery  is  to  be  washed  away,  and  some  of  the  finer  kind  substi¬ 
tuted  ;  and  so  on  through  three  or  four  different  degrees  of  fine¬ 
ness,  until  all  the  roughnesses  and  apparent  scratches  on  the 
glass  are  worn  down,  and  it  has  become  perfectly  smooth  to  the 
touch,  although  dull  and  opaque  to  the  eye:  after  this  it  is 
sometimes  further  ground  with  finely  pounded  pumice-stone. 

At  the  expiration  of  every  five  or  six  minutes,  during  this 
grinding  process,  the  surface  of  the  tool  is  rubbed  for  a  short 
time  within  the  concave  tool,  that  its  proper  curvature  may  be 
perfectly  preserved.  When  the  operation  has  been  completed, 
the  glass  is  easily  separated  from  its  wooden  handle  by  means 
of  a  thin  knife,  and  the  pitch  is  removed  by  rubbing  it  with  oil. 
The  side  which  has  been  ground  is,  in  its  turn,  fixed  upon  the 
wooden  handle,  and  the  other  side  is  then  ground  in  the  same 
manner  as  the  first. 

Convex  glasses  are  frequently  prepared  for  common  purposes, 


CHAP.  X. 


POLISHING  LENSES.  191 

in  another  manner.  The  concave  tool  is  fixed  upon  the  lathe 
and  the  glass  being  held  steadily  in  the  hand,  and  sprinkled 
with  emery,  is  applied  to  the  tool  during  its  revolutions.  For 
concave  glasses,  the  convex  tool  is  fitted  to  the  lathe,  and  the 
glass  is  in  like  manner  presented  to  it ;  but  this  method,  although 
easier  and  more  expeditious,  is  greatly  inferior  in  its  result  to 
hand-grinding,  and  cannot  be  resorted  to  when  any  thin"  like 
perfectness  in  the  intended  instrument  is  desired. 

The  same  brass  tool  which  is  used  for  grinding,  serves  also 
for  polishing  lenses;  but  before  it  is  thus  employed,  a  smooth 
tlnck  piece  of  felt  must  be  stretched  over  and  cemented  to  it 
and  the  outer  surface  being  then  covered  with  washed  putty 
powder,  which  is  a  combination  of  the  oxides  of  tin  and  lead 
the  tool  is  worked  upon  the  lens  with  the  same  motions  as  are 
employed  m  grinding  it.  The  consistency  of  the  powder  is  a 
point  retiring  attention;  for  if  it  be  too  moist,  it  will  cause 
the  fibres  of  the  felt  to  rise  up  and  polish,  not  only  the  surface, 
aroperly  speaking,  but  likewise  the  innumerable  hollows,  which, 
lot  withstanding  all  appearances  to  the  contrary,  are  actually 
eft  m  the  surface  from  the  grinding.  If  the  lens  be  subjected 
■o  examination  in  a  microscope,  this  effect  will  be  rendered 
tiny  apparent.  The  evil  consequence  resulting  from  this  de- 
ect  is,  that  the  cavities  being  polished,  admit  the  rays  of  light 
und  disperse,  instead  of  collecting  them,  as  would  be  the  case 
t  the  surface  were  uniform.  When  this  fault  exists  in  a  de¬ 
cree  so  exaggerated  as  to  be  visible  to  the  naked  eye,  the  lens 
s  said  to  be  curdled. 

An  excellent  method  has  lately  been  adopted  by  an  eminent 
ptician  in  London,  whereby  this  defect  is  avoided.  Bees’ 
rax  is  hardened  to  a  proper  degree  by  admixture  with  dry  red 
ulphate  of  iron,  which  has  previously  been  carefully  washed ; 
nd  instead  of  the  covering  of  felt,  this  compound  is  melted 
ver  the  brass  tool.  When  cold,  the  casing  thus  formed  is  suf- 
ciently  hardened  to  be  turned  to  the  required  curvature,  and 
1  tt!00  ’  waen  this  ^as  been  done,  is  in  a  fit  state  for  use. 

riie  peculiar  advantage  of  this  compound,  as  a  polishing 
lbstance,  consists  in  its  perfect  uniformity;  besides  which,  it 
as  this  further  recommendation,  that  if  any  hard  particles 
lould  accidentally  insinuate  themselves  between  the  tool  and 
ie  lens,  and  which  m  other  circumstances  would  scratch  the 
lass,  the  wax  is  sufficiently  yielding  to  allow  them  to  bury 
lemselves  in  its  substance,  so  that  all  injury  of  this  kind  is 
raided. 

Lenses  which  have  been  thus  treated,  will  bear  examination 
^a^microscoPe)  their  polish  appearing  uniformly  clear  and 


X92  GLASS  MANUFACTURE.  CHAP.  X. 

Convex  lenses  in  their  simple  state  have  been  used  for  col- 
lectin"  the  heating  rays  of  the  sun,  or  for  forming  what  are 
called” burning-glasses.  One  of  the  largest  lenses  ever  appfied 
to  this  purpose  was  made  of  flint  glass  by  Mr.  Parker.  I  he 
diameter  of  this  glass  was  3  feet ;  its  focal  distance  was  45 
inches ;  and  the  circular  spot  of  light  which  it  cast  at  the  focal 
point  wTas  1  inch  in  diameter.  Still  farther,  and  as  much  as 
possible  to  condense  the  rays,  Mr.  Parker  employed  a  smaller 
lens,  13  inches  in  diameter,  in  conjunction  with  the  larger  one, 
and  by  means  of  this  the  heating  rays  were  concentrated  at 
the  focal  point  to  f  of  an  inch.  The  effects  produced  by  this 
arrangement  were  surprising:  20  grains  of  pure  gold  were 
fused  in  4  seconds ;  the  same  effect  was  produced  on  10  grains 
of  platina  in  3  seconds ;  and  a  diamond,  whose  weight  was  10 
grains,  was  found  to  have  lost  4  grains  after  having  been  placed 
within  the  focus  during  30  minutes. 

This  lens,  which  cost  700/.,  has  since  passed  into  the  posses¬ 
sion  of  the  emperor  of  China. 


CHAP.  XI. 

ON  THE  PRINCIPAL  DEFECTS  OBSERVABLE  IN  GLASS. 

Stria:—  Render  Glass  unfit  for  Optical  Purposes.— Threads— Render  Glass 
fragile.— Cause  of  this.— Tears— One  of  the  greatest  Defects.— Render 
Glass  useless.— Knots.— Bubbles.— Whence  they  proceed.— Do  not  much 
affect  the  duality  of  Glass.— Objects  to  be  attained  for  avoiding  these  De¬ 
fects.— M.  Guinand.— His  humble  Origin.— Energy  of  Character.— Exam 
ines  Telescopes,  and  constructs  others.— Unable  to  procure  Glass  of  good 
Quality.— Is  incited  to  examine  into  the  Causes  of  Inferiority.— His  ex 
traordinary  Perseverance  amidst  Accidents  and  Difficulties.— His  ultimate 
Success.— Accident  leading  to  further  Improvement— Prosecutes  Ins  art 
in  Bavaria.— Returns  to  Switzerland,  and  further  pursues  his  favorite  Ob¬ 
ject. _ Dies. — Frauenhofer. — Rises  from  Obscurity  by  his  Talents.— His 

Scientific  Acquirements.— Produces  Specimens  of  perfect  Glass.— Dies  at 
an  early  Age.— Respect  paid  to  his  Memory. 

The  principal  defects  observable  in  manufactured  glass,  are 
strife,  threads,  tears,  and  knots.  These,  when  they  occur  to 
any  extent,  all  impair  its  beauty,  and  some  of  them  injure  itSi 
actual  quality.  Although  it  is  not  difticult  to  attain  such  an 
amount  of  proficiency  in  the  manufacture  as  will  preserve  the 
materials  from  these  evils  in  their  extreme  degree,  yet,  alto-i 
gether  to  avoid  their  occurrence,  and  to  obtain  glass  of  a  per-; 
feet  quality,  is  a  task  that  long,  and  with  only  doubtful  success,! 
has  engaged  the  thoughts  and  labors  of  men  devoted  to  scien-j 
tific  pursuits.  The  difficulties  that  attend  the  attainment  of 
this  object  arc  sufficiently  proved  by  the  fact  that,  during  ten 
years,  one  of  the  most  considerable  and  most  scientific  opticians 


CHAP.  XI. 


DEFECTS  IN  GLASS. 


193 


in  London  has  been  disappointed  in  his  efforts  to  procure  a  disc 
of  flint  glass  only  five  inches  in  diameter,  sufficiently  fitted,  by 
the  absence  of  defects,  to  be  employed  in  the  construction  of  a 
telescope. 

Striae  are  undulating  appearances,  perfectly  vitrified,  and 
equally  transparent  with  any  other  part  of  the  glass :  they  do 
not  occasion  any  roughness  or  inequality  in  the  surface,  but  re¬ 
sult  from  a  want  of  congruity  in  the  composition  of  the  parti¬ 
cles  which  make  up  the  substance :  in  other  words,  the  struc¬ 
ture  is  not  perfectly  homogeneous ;  and  although  each  different 
portion  may  be  altogether  good  in  itself,  and  the  whole  mass, 
if  made  up  of  any  one  of  these  portions,  would  be  equally  per¬ 
fect  in  itself,  yet,  the  whole  acting  without  any  uniformity,  the 
rays  of  light  in  passing  through  them  are  bent  or  refracted 
differently,  and  the  objects  beyond  appear  distorted. 

This  condition  must  exist  to  a  considerable  extent  to  be  easi¬ 
ly  discernible  by  the  naked  eye,  or  detrimental  to  the  quality 
of  the  glass,  when  applied  to  the  more  ordinary  purposes  of 
use  or  ornament ;  but  glass  striated  in  a  scarcely  perceptible 
degree,  is  yet  wholly  inapplicable  to  the  construction  of  optical 
instruments,  where  the  objects  they  are  intended  to  present  to 
the  eye  will  be  many  times  magnified ;  and  where,  consequent¬ 
ly,  every  defect  or  distortion  that  accompanies  their  transmis¬ 
sion  through  the  glass  will  be  equally  enlarged.  The  end  pro¬ 
posed  in  the  employment  of  these  philosophical  instruments,  is 
the  minutely  accurate  examination  of  distant  or  very  diminu¬ 
tive  objects ;  and  this  purpose  it  is  evident  must  be  completely 
frustrated,  by  the  defect  here  described. 

The  name  of  threads  is  usually  given  to  fibrous  appearances 
in  the  body  of  the  glass,  which  result  from  the  vitrification  of 
clay.  Their  color  is  greener  than  that  of  the  rest  of  the  glass. 
Threads,  if  existing  in  great  numbers,  render  the  material  ex¬ 
tremely  fragile ;  and  the  same  effect  is  produced,  if,  although 
fewer  in  number,  the  threads  are  individually  larger.  The 
cause  of  this  increased  brittleness  is,  that  the  dilation  and  con¬ 
traction,  at  different  temperatures,  of  glass,  which  results  from 
tire  fusion  of  clay,  differ  from  those  of  glass  made  with  silice¬ 
ous  sand ;  for  which  reason,  each  in  turn  exerts  a  hurtful  influ¬ 
ence  upon  the  other. 

Tears  are,  perhaps,  the  greatest  defect  that  can  be  found  in 
glass.  They  are  in  fact  an  exaggeration  of  the  imperfection 
last  described,  and  usually  proceed  from  the  fusion  and  vitrifi¬ 
cation  of  portions  of  the  clay  that  forms  the  arch  of  the  fur¬ 
nace,  and  which  are  suffered  to  drop  into  the  pots,  and  to  float 
in  the  glass  while  in  its  state  of  fusion.  Wherever  these  tears 
exist,  the  material  is  brittle  in  a  very  high  degree,  so  as  fre- 


194 


GLASS  MANUFACTURE. 


CHAP.  XI. 


quently  to  crack,  without  any  apparent  cause,  by  the  mere  ef¬ 
fect  of  the  unequal  expansion  just  described,  which  accident  is 
more  likely  to  occur  in  proportion  as  the  drops  are  nearer  to 
the  surface.  This  defect  is  one  of  so  serious  a  nature,  that  it 
is  usual,  on  discovering  its  existence,  at  once  to  throw  aside 
the  glass  as  useless.  In  places  where,  as  is  frequently  the  case 
in  England,  covered  crucibles  are  employed,  this  accident  is  in 
a  great  degree  avoided. 

Three  kinds  of  knots  are  observable  in  glass ;  one  of  these 
arises  from  the  aggregation  of  several  imperfectly  vitrified 
grains  of  sand.  Another  is  owing  to  some  portions  of  glass 
gall  not  having  been  removed  during  the  refining;  and  the 
third  kind  is  produced  by  any  small  parts  of  the  crucible  or  of 
the  furnace  which,  having  been  abraded  by  the  rubbing  of  the 
tools  or  other  accidental  circumstance,  have  fallen  into  the 
glass. 

Small  bubbles  are  frequently  seen  abundantly  spread  through¬ 
out  the  substance  of  the  glass.  These  indicate  an  imperfect 
degree  of  refining,  and  proceed  from  the  disengagement  of 
gas  which  occurs  during  the  process  of  vitrification.  Their 
presence  announces  that  the  glass  has  not  been  sufficiently  fluid 
in  the  course  of  its  refining  to  allow  of  their  dispersion.  This 
may  happen  through  one  of  two  causes,  either  that  a  sufficient 
amount  of  fluxing  material  has  not  been  used  with  the  sand, 
or  that  the  fire  has  not  been  sufficiently  intense  for  the  due 
liquefaction  of  the  compound.  These  bubbles  are  chiefly  ob¬ 
jectionable  on  account  of  their  unsightly  appearance,  and  do 
not  really  deteriorate  the  quality  of  the  glass  even  for  optical 
purposes.  In  this  case  each  bubble  acts  as  a  small  convex  lens, 
rapidly  turning  aside  the  rays  which  strike  against  it,  and  oc¬ 
casioning  a  diminution  of  light  in  proportion  to  its  area.  But 
when  these  bubbles  are  even  numerous,  the  sum  of  their 
united  areas  will  amount  to  only  a  small  proportion  of  the 
whole  surface  of  the  glass;  and  the  loss  of  light  will  be  incon¬ 
siderable.* 

It  thus  appears  that  the  principal  object  to  be  sought  after  in 
the  manufacture  of  perfectly  homogeneous  glass  is,  to  avoid 
those  variations  in  the  composition  and  specific  gravity  of  its 
different  parts,  which  occasion  the  striated  appearance  de¬ 
scribed  above.  To  enter  minutely,  and  at  length,  into  a  con¬ 
sideration  of  the  means  that  have  been  proposed  and  adopted 
with  a  view  to  remedy  this  considerable  evil,  would  present 
little  that  is  amusing  to  the  general  reader ;  while  those  per¬ 
sons  who  feel  any  particular  interest  in  the  subject,  or  whose 


*  R*r  Faraday,  Bakerian  Lect. ;  Phil.  Trans.  1830,  p. 


CHAP.  XI. 


M.  GUINAND. 


195 


taste  for  scientific  research  leads  them  to  admire  the  detail  of 
well  considered  and  ably  conducted  plans  for  the  mastery  of  a 
difficult  operation,  may  gratify  themselves  by  consulting  Mr. 
Faraday’s  truly  valuable  paper  already  referred  to,  and  which 
will  be  found  comprised  in  the  Philosophical  Transactions  for 
the  year  1830. 

Some  exceedingly  favorable  specimens  of  glass  for  optical 
purposes  have  lately  been  prepared  by  Mr.  Green,  the  proprie¬ 
tor  of  the  Stangate  Glass-house ;  a  gentleman  whose  personal 
attention  has  been  unintermittingly  given  during  many  years 
to  all  the  practical  operations  and  details  of  an  extensive  es¬ 
tablishment.  Mr.  Green  is  far  from  asserting  that  in  what  has 
been  accomplished  he  has  arrived  at  any  certainty  in  the  solu¬ 
tion  of  this  difficult  problem,  and  feels  that  at  most  he  has 
hitherto  made  only  an  approach  to  it;  while,  however,  it  is 
such  an  approach  as  justifies  the  hope,  that,  through  continued 
thought  and  exertion,  a  still  greater  and  more  important  de¬ 
gree  of  perfection  may  be  attained. 

The  circumstances  which  attended  the  long-continued  and 
laborious  investigations  on  this  subject  of  another  and  a  very 
extraordinary  man,  are,  in  themselves,  so  curious  and  interest¬ 
ing,  and  seem  likely  to  be  followed  by  such  important  conse¬ 
quences,  to  at  least  one  branch  of  the  art,  that  a  treatise  on  the 
manufacture  of  glass  might  be  justly  charged  with  incomplete¬ 
ness,  if  it  did  not  furnish  at  least  a  sketch  of  those  circum¬ 
stances. 

The  following  account  is  condensed  from  a  memoir,  read  at 
a  sitting  of  the  Society  of  Physics  and  Natural  History  of  Ge¬ 
neva,  on  the  19th  of  February,  1823,  as  given  in  the  nineteenth 
volume  of  the  Quarterly  Journal  of  Science,  published  in  Lon¬ 
don  in  the  year  1825. 

The  late  M.  Guinand  was  born  in  an  inconsiderable  village, 
among  the  mountains  of  Neufchatel  in  Switzerland.  His  father 
was  by  trade  a  joiner,  and  must  have  been  in  very  indifferent 
circumstances,  as  his  son  was  called  upon  to  assist  him  when 
only  ten  years  old,  and  without  having  acquired  more  than  a 
very  imperfect  knowledge  of  the  first  rudiments  of  learning  ; 
a  deficiency  which  was  never  afterwards  supplied,  as  M.  Gui¬ 
nand  always  read  with  difficulty,  and  wrote  very  imperfectly. 
He  must,  even  at  this  early  period,  have  been  a  lad  of  consid¬ 
erable  talent,  and  of  a  disposition  that  urged  him  to  the  exer¬ 
tion  requisite  for  raising  his  condition  in  society.  We  find 
him,  when  between  thirteen  and  fourteen  years  old,  having 
quitted  the  employment  of  a  joiner  for  that  of  a  cabinet-maker, 
chiefly  engaged  in  making  cases  for  clocks.  At  this  period  he 
acquired  from  an  acquaintance  some  knowledge  of  the  art  of 


196 


GLASS  MANUFACTURE. 


CHAP.  XI. 


casting  and  working  in  metals,  of  which  knowledge  lie  after¬ 
wards  availed  himself  by  adopting,  when  twenty  years  of  age, 
the  occupation  of  a  watch-case  maker,  the  manufacture  of 
watches  forming  a  very  considerable  branch  of  industry  in  that 
part  of  the  country. 

At  the  house  of  a  person  for  whom  he  then  worked,  M.  J. 
Droz,  the  constructor  of  several  automaton  figures,  which  forty 
years  ago  made  the  tour  of  Europe,  young  Guinand  enjoyed 
an  opportunity  of  seeing  for  the  first  time  a  very  fine  reflecting 
telescope  which  had  been  made  in  England,  and  which  at  once 
appeared  to  him  so  curious  and  interesting  an  object,  that  he 
petitioned  for  and  obtained  leave  to  take  it  in  pieces,  the  more 
minutely  to  examine  its  construction.  The  use  made  of  this 
permission  was  soon  rendered  apparent  by  the  production  of  a 
similar  telescope ;  and  this,  which  he  had  constructed  with  his 
own  hands,  on  being  examined  by  many  competent  persons, 
was  pronounced  by  them  to  be  equal  in  excellence  to  that 
which  had  served  him  as  a  pattern. 

Surprised  at  this  success,  the  gentleman  to  whose  kindness 
he  owed  this  opportunity  questioned  the  artist  as  to  his  ac¬ 
quaintance  with  the  science  of  optics,  and  in  particular  to  what 
treatise  he  was  indebted  for  his  proficiency.  The  surprise  of 
M.  Droz  was  naturally  increased  on  learning  that  the  instru¬ 
ment  had  been  produced  without  any  knowledge  whatever  of 
the  theory  of  optics,  and  with  no  more  acquaintance  with  the 
practice  of  the  art  than  had  been  acquired  through  the  exam¬ 
ination  of  the  English  instrument.  M.  Droz  immediately  placed 
a  treatise  on  the  subject  in  the  hands  of  the  young  man,  which 
he  rather  deciphered  than  read ;  but  the  substance  of  which 
was  imbibed  by  him  so  completely,  that  he  was  enabled,  after 
witnessing  the  making  of  one  pair  of  spectacles,  to  form  and 
polish  lenses,  and  to  make  spectacles  for  himself  and  others, 
which  were  pronounced  to  be  excellent.  His  principal  amuse¬ 
ment  at  this  time  was  found  in  manufacturing  telescopes,  which 
he  got  up  at  a  cheap  rate,  forming  the  tubes  of  pasteboard. 

When  the  important  discovery  of  achromatic  glasses  reached 
<  Switzerland,  Guinand’s  mind  was  very  strongly  excited  by  it ; 
and  M.  Droz  having  obtained  a  telescope  of  the  new  construc¬ 
tion,  again  permitted  the  young  man  to  examine  its  various 
parts  and  structure.  The  very  imperfect  state  of  the  arts  at 
that  time  in  Switzerland,  and  the  deficient  means  of  Guinand, 
prevented  his  achieving  the  construction  of  a  similar  instru¬ 
ment.  He  was  unable  to  produce  glasses  of  different  refractive 
power ;  and  it  was  not  until  several  years  after  that  an  ac¬ 
quaintance,  making  a  visit  to  England,  conveyed  to  him  a  piece 
of  flint  glass,  with  which,  although  it  was  by  no  means  void  of 


CHAP.  XI.  M.  GUINAND.  197 

imperfections,  being  considerably  striated,  he  succeeded  in 
making  some  tolerably  good  achromatic  glasses.  Finding  that 
not  only  the  glass  which  lie  had  himself  worked,  but  that  every 
other  specimen  which  he  examined  was  thus  imperfect,  he  was 
incited  to  a  more  particular  scrutiny  into  the  subject,  and  bring¬ 
ing  into  action  all  the  knowledge  he  had  acquired  in  the  art  of 
fusion,  he  melted  in  his  furnace  the  fragments  of  his  flint  glass. 
All  the  satisfaction  derived  from  this  experiment  was  the  ac¬ 
quirement  of  some  degree  of  knowledge  as  to  the  composition 
of  flint  glass,  some  particles  of  lead  being  revived  in  the  metal¬ 
lic  state  during  the  process.  Guinand  was  thirty-five  years  old 
at  the  time  when  this  fresh  incitement  led  to  his  seeking  after 
such  chemical  knowledge  as  might  assist  him  in  experiments 
on  vitrification,  and  his  evenings’  employment  during  six  or 
seven  years  was  to  melt  in  his  blast  furnace  a  few  pounds’ 
weight  of  glass,  carefully  noting  down  every  circumstance  at¬ 
tending  each  experiment,  that  he  might  be  enabled  to  continue 
such  as  afforded  any  prospect  of  advantage,  and  to  avoid  others 
which  had  a  contrary  tendency. 

•  These  small  experiments  led  to  no  decisive  results ;  and  he 
was  upwards  of  forty  years  old  when,  having  undertaken  a 
new  and  more  profitable  trade,  that  of  making  bells  for  repeat¬ 
ing-watches,  he  was  enabled  to  devote  more  of  his  earnings  to 
the  prosecution  of  experiments,  which  he  thenceforth  under¬ 
took  upon  a  scale  more  likely  by  their  results  to  reward  his 
perseverance. 

In  this  pursuit  he  was  still  exposed  to  numerous  accidents 
and  difficulties,  which  would  have  deterred  most  persons  from 
continuing  the  research.  His  furnace,  which  lie  had  con¬ 
structed  with  his  own  hands,  out  of  such  materials  as  he  could 
procure,  and  which  was  capable  of  melting  at  once  200  lbs. 
weight  of  glass,  proved  defective.  He  was  then  obliged  to  pro¬ 
cure  materials  for  the  purpose  from  abroad  ;  and  having  once 
more  completed  its  erection,  and  consumed  much  fuel  in  heat¬ 
ing  it,  had  the  mortification  to  find  that  it  still  required  altera¬ 
tion.  Then  his  crucibles,  which  he  was  equally  obliged  to  form 
with  materials  ill-qualified  for  the  object,  cracked  during  the 
process,  and  the  vitreous  matter  was  lost  among  the  ashes  of 
his  furnace.  Although  during  all  this  time  his  family  arrange¬ 
ments  were  formed  upon  a  plan  of  the  most  rigid  economy,  he 
was  compelled  to  employ  an  interval  between  each  one  of  his 
experiments  in  earning  at  his  regular  employment  sufficient 
means  for  subsistence,  and  for  providing  the  apparatus,  mate¬ 
rials*  and  fuel  needful  for  renewing  them. 

All  this  time  the  pursuit  had  laid  hold  so  completely  of  his 
mind,  that  he  was  deprived  of  his  natural  rest  while  considering 

R  2 


198  GLASS  MANUFACTURE.  CHAP.  XI. 

upon  the  causes  of  his  various  failures,  and  endeavoring  to  rea¬ 
son  out  the  means  for  their  prevention. 

Having  at  length  succeeded  in  obtaining  a  block  of  glass 
weighing  about  2(J0  pounds,  and  having  sawn  it  into  two  verti¬ 
cal  sections,  he  polished  one  of  the  faces,  in  order,  as  far  as 
possible,  to  examine  the  circumstances  produced  by  the  fusion. 

To  account  for  the  numerous  and  various  defects  exhibited 
by  this  specimen,  M.  Guinand  formed  a  theory  which  he  made 
the  groundwork  of  his  future  operations.  A  more  intimate 
knowledge  of  those  defects,  and  a  conviction  thus  attained  of 
the  great  difficulties  opposed  to  their  removal,  instead  of  damp¬ 
ing  his  ardor  in  the  pursuit,  served  to  infuse  new  energy  into 
his  mind.  Nor  was  he  mistaken  in  his  estimate  of  the  obstacles 
to  be  surmounted ;  “  so  that,”  as  he  himself  declared,  “  the 
sacrifices  and  exertions  which  he  had  previously  made  were 
trifling  when  compared  with  those  which  he  afterwards  under¬ 
went  for  the  purpose  of  removing  these  various  defects,  and  of 
rendering  his  glass  homogeneous.” 

The  steps  through  which  he  pursued  this  arduous  under¬ 
taking,  and  the  methods  by  which  its  success  was  accomplished, 
it  is  not  possible  to  detail.  All ‘that  is  publicly  known  upon  the 
subject  is,  that  he  succeeded  in  discovering  a  mode  of  proceed¬ 
ing  which  gave  the  almost  certainty  of  producing  in  the  fusion 
of  a  pot  containing  from  200  to  400  pounds  of  glass,  one  half 
at  least  of  its  substance  entirely  homogeneous,  and  therefore 
fitted  for  the  construction  of  perfect  optical  instruments.  With 
this  result,  satisfactory  as  it  would  have  been  to  most  men, 
Guinand  expressed  himself  by  no  means  contented,  and  con¬ 
tinued  his  researches,  without,  however,  ever  arriving  much 
nearer  to  perfection  in  the  art. 

He  was  now  enabled  to  make  for  use  discs  of  glass  perfectly 
homogeneous,  with  a  diameter  of  twelve  inches;  a  great 
achievement,  when  compared  with  what  had  been  at  any  time 
accomplished  by  others. 

On  one  occasion  the  artist  had  succeeded,  through  much 
carefulness  and  exertion,  in  obtaining  a  disc  eighteen  inches  in 
diameter,  and  of  a  quality  perfectly  satisfactory.  This  was  al¬ 
ready  finished  and  placed  in  the  annealing  oven  to  cool  gradu¬ 
ally,  when,  through  some  unaccountable  accident,  the  fire 
caught  the  roof  of  his  humble  dwelling.  With  some  trouble 
the  flames  were  extinguished  ;  but  the  water  used  for  this  pur¬ 
pose  had  found  its  way  into  the  oven,  and  the  precious  deposit 
was  destroyed.  It  is  said  that  the  discouragement  caused  by 
this  accident  prevented  M.  Guinand  from  afterwards  attempting 
any  similarly  extensive  experiment.  He  entertained  no  doubt, 
however,  that,  with  means  for  operating  on  a  larger  scale  than 


M.  GUINAND. 


CHAP.  XI. 


199 


he  could  accomplish,  lensc9  of  double  or  even  triple  the  diame¬ 
ter  here  mentioned  might  be  produced. 

For  some  time  after  he  had  thus  far  succeeded  in  his  object, 
M.  Guinand  was  accustomed  to  divide  his  blocks  of  glass  by 
that  which  appeared  the  only  fitting  method,  sawing  them  into 
sections  perpendicular  to  their  axis,  polishing  the  sections,  and 
then  selecting  such  parts  as  were  adapted  to  his  purpose,  re¬ 
turning  the  remaining  portions  to  the  crucible  for  future  opera¬ 
tions.  By  this  means  he  had  frequently  the  mortification  of  per¬ 
ceiving  that  the  glass  was  divided,  so  as  to  present  a  less  ex¬ 
tended  surface  of  perfect  material  than  the  state  of  the  block 
would,  if  previously  known,  have  rendered  possible;  and  he 
was  frequently  able  to  procure  discs  of  only  small  diameter, 
when,  could  he  have  been  fully  aware  of  the  particular  circum¬ 
stances  of  the  glass  throughout  its  substance,  he  might,  by  cut¬ 
ting  in  another  direction,  have  obtained  a  more  satisfactory  re¬ 
sult. 

This  disadvantage  was  remedied  in  a  way  apparently  as  un¬ 
toward  as  it  was  singular  and  unexpected.  While  his  men 
were  one  day  carrying  a  block  of  glass  on  a  hand-barrow  to  a 
water  saw-mill,  which  he  had  constructed  at  the  fall  of  the 
river  Doubs,  a  short  distance  from  his  dwelling,  the  mass  acci¬ 
dently  slipped,  and,  rolling  to  the  bottom  of  a  rocky  declivity, 
was  broken  into  several  pieces.  Endeavoring  to  make  the  best 
of  this  seeming  misfortune,  such  fragments  of  glass  were  se¬ 
lected  for  operation  as  appeared  to  be  fitted  by  their  homoge¬ 
neity  for  the  purpose;  and  these  were  softened  in  circular 
moulds,  in  such  a  manner  that  they  furnished  discs  of  a  very 
satisfactory  quality.  Further  examination  enabled  Guinand  to 
perceive  that  the  fracture  had  in  a  great  measure  followed  the 
variations  of  density  in  the  glass ;  and,  pursuing  the  idea  thus 
obtained,  the  artist  thenceforth  adhered  to  a  method  so  singu¬ 
larly  in  the  first  instance  forced  upon  him. 

After  this,  M.  Guinand  contrived  a  mode  of  cleaving  the 
glass  while  cooling,  so  that  the  fracture  accompanied  the  direc¬ 
tion  of  the  more  faulty  parts ;  by  which  course  he  frequently 
obtained  masses  of  glass  which  were  absolutely  homogeneous, 
weighing  from  forty  to  fifty  pounds.  These  masses,  cleft  again 
by  means  of  wedges  into  pieces  of  convenient  shape,  were  re¬ 
melted  in  moulds  which  gave  them  the  form  of  discs ;  an  ope¬ 
ration  which  differs  essentially  from  that  used  by  other  glass- 
makers. 

Several  years  of  his  life  were  thus  employed  by  this  extraor¬ 
dinary  man  in  making  bells  for  repeating-watches,  and  con¬ 
structing  achromatic  telescopes  with  glass  of  his  own  prepar¬ 
ing.  The  retired  spot  wherein  he  resided,  offered  only  very 


200 


GLASS  MANUFACTURE. 


CHAP.  XI. 


limited  opportunities  for  acquiring  a  reputation  in  the  world ; 
yet,  by  degrees,  the  superior  value  of  his  labors  became  appre¬ 
ciated,  and  he  was  visited  by  such  men  of  science  as  travelled 
into  the  neighborhood  of  his  dwelling.  By  one  of  these,  a 
knowledge  of  his  merits  was  conveyed  to  M.  Frauenhofer,  the 
chief  of  a  celebrated  manufactory  for  optical  instruments,  es¬ 
tablished  at  Benedictbeurn  in  Bavaria.  This  gentleman  having 
in  consequence  obtained  some  discs  of  glass  made  by  Guinand, 
found  their  quality  so  satisfactory,  that  he  repaired  in  person  to 
Brenets,  where  the  artist  resided,  and  engaged  him  to  settle  in 
Bavaria.  This  was  in  1805,  when  Guinand  was  upwards  of 
sixty  years  of  age.  He  continued  at  Benedictbeurn  during  nine 
years,  occupied  solely  in  the  manufacture  of  glass,  to  the  great 
increase  of  M.  Frauenhofer’s  reputation. 

Being  desirous,  at  the  end  of  this  time,  to  return  to  his  native 
land,  a  pension  was  granted  to  him  by  the  establishment,  on 
condition  that  he  should  no  longer  employ  himself  in  making 
glass,  nor  disclose  his  process  to  any  person  whatever  ;  a  con¬ 
dition  which  did  not  long  agree  with  the  still  active  energies 
of  his  mind.  Believing  that  by  new  experiments  he  could  raise 
his  discovery  to  a  yet  higher  degree  of  improvement,  he  obtain¬ 
ed  the  consent  of  M.  Frauenhofer  to  cancel  their  subsisting 
agreement ;  and  relinquishing  his  pension,  once  again  devoted 
himself  with  ardor  to  his  favorite  pursuit. 

M.  Guinand  lived  for  several  years  after  this  time  (1816,) 
and  produced  several  telescopes  of  great  magnitude,  and  re¬ 
markable  for  their  excellence ;  it  being  perhaps  not  the  least 
extraordinary  among  the  circumstances  attending  them,  that, 
to  use  the  words  of  the  memoir,  whence  the  foregoing  account 
is  drawn,  “  they  have  been  constructed  by  an  old  man  upwards 
of  seventy,  who  himself  manufactures  the  flint  and  crown  glass 
which  he  uses  in  their  construction,  after  having  made  with  his 
own  hands  the  vitrifying  furnace  and  his  crucibles;  who,  with¬ 
out  any  mathematical  knowledge,  devises  a  graphic  method  of 
ascertaining  the  proportions  of  the  curves  that  must  be  given 
to  the  lenses,  afterwards  works  and  polishes  them  by  means  pe¬ 
culiar  to  himself;  and  lastly,  constructs  all  the  parts  of  the  dif¬ 
ferent  mountings,  either  with  joints  or  on  stands,  melts  and 
turns  the  plates,  solders  the  tubes,  prepares  the  wood,  and  com¬ 
pounds  the  varnish.” 

Arrangements  had  been  made  by  the  French  government 
for  purchasing  his  secret,  when  the  artist,  verging  on  his  eigh¬ 
tieth  year,  died,  after  a  short  illness.  That  secret  did  not,  how¬ 
ever,  die  with  him,  but  is  possessed  by  his  son,  who  continues 
to  labor  in  the  employment  so  singularly  commenced,  and  so 
successfully  and  energetically  followed  by  his  father. 


CHAP.  XI. 


M.  GUINAND. 


201 

The  name  of  Frauenhofer,  which  has  been  introduced  in  the 
foregoing  narrative,  is  one  intimately  connected  with  inquiries 
in  the  art  of  making  perfect  glass.  It  would  be  wrong  to  leave 
the  reader  under  an  impression  that  the  merit  of  this  artist  was 
limited  to  the  single  act  of  patronage  extended  towards  Gui- 
nand,  and  which,  although  indicative  of  his  discernment  as  a 
tradesman,  would  afford  no  reason  for  investing  him  with  any 
part  of  the  extraordinary  merit  which  truly  belonged  to  his 
character. 

Like  Guinand,  his  beginning  in  life  was  humble ;  being  in¬ 
debted  solely  to  the  powers  of  his  own  mind  for  the  eminence 
to  which  he  attained.  Having  occupied  the  lowest  station  as  an 
ordinary  workman  in  a  great  manufacturing  establishment,  he, 
by  the  force  of  his  transcendent  talents,  and  in  the  course  of  a 
few  years,  raised  himself  to  the  chief  direction  of  its  business. 
During  the  intervals  of  labor  he  acquired  a  competent  know¬ 
ledge  of  mathematical  science ;  and  devoting  himself  to  the  per¬ 
fection  of  the  refracting  telescope,  proved  that  he  possessed  a 
truly  philosophical  and  scientific  mind.  Having  soon  mastered 
the  theoretical  difficulties  which  presented  themselves,  he  still, 
however,  found  all  his  labors  unavailing,  through  the  imperfec¬ 
tion  of  the  material  employed ;  and  set  himself  to  remedy  this 
evil,  by  a  series  of  admirable  experiments. 

It  might  be  thought  invidious  to  inquire  in  what  degree  his 
success  in  these  was  owing  to  the  previous  labors  and  assist¬ 
ance  of  Guinand,  or  how  far  his  discoveries  were  personal  and 
original.  Both  produced  and  left  behind  them  specimens  of 
perfect  glass  in  large  pieces ;  but  the  public  has  equally  in 
either  case  to  regret  the  want  of  knowledge  as  to  the  processes 
employed  for  the  attainment  of  an  object  so  desirable. 

Frauenhofer  died  in  the  year  1826,  at  an  early  age ;  a  victim, 
it  is  said,  to  unremitting  attention  bestowed  upon  an  unhealthy 
employment.  Had  his  life  been  continued  to  the  same  length¬ 
ened  period  as  was  allotted  to  his  fellow-laborer,  what  might 
not  the  world  have  expected  from  one,  who  so  early  had  burst 
tbe  chains  of  ignorance,  and  overcome  the  paralyzing  difficul¬ 
ties  of  birth  and  adverse  fortune ;  taking  his  station  during 
life  among  the  genuine  philosophers  of  the  age,  and  falling, 
admired,  and  lamented,  and  eulogized  by  the  most  scientific 
societies  of  Europe  ! 

Tbe  great  value  of  flint  glass,  from  which  all  perceptible 
defects  are  absent,  may  be  imagined  from  the  sketch  which 
has  here  been  given  of  the  efforts  made  for  its  production. 
Very  high  prices  are,  in  fact,  paid  for  object  glasses  of  a  satis¬ 
factory  quality,  which  are  of  any  magnitude ;  while  even  small 
fragments  of  such  glass  are  sought  after  by  opticians  with 


GLASS  MANUFACTURE. 


CIIAP.  XI. 


202 

great  avidity.  A  few  years  ago  the  director  of  one  of  the 
London  glass-houses  having  made  a  pot  of  flint  glass  for  optical 
purposes,  sold  this,  in  the  regular  course  of  his  business,  to  a 
commission  merchant,  who  transmitted  it  to  his  correspondent 
on  the  Continent.  Some  months  having  elapsed  thereafter, 
during  which  time  its  possessor  had  ascertained  the  true  value 
of  his  purchase,  the  manufacturer  was  surprised  at  receiving 
numerous  inquiries  on  the  subject  of  this  lump  of  glass,  on  the 
part  of  several  English  opticians.  These  were  anxious  to  pro¬ 
cure  portions  of  a  material,  the  fame  of  which  had  reached 
them  from  abroad.  Upon  this,  the  maker  instituted  a  search, 
and  having  succeeded  in  identifying  some  fragments,  as  having 
formed  part  of  the  same  melting,  was  enabled  to  procure  very 
considerable  prices  for  that  upon  which  he  had  previously  set 
little  or  no  value,  and  which  had  been  preserved  only  through 
accident. 

On  a  yet  more  recent  occasion,  information  having  reached 
London  that  a  large  and  superior  object  glass  was  on  sale  in 
the  metropolis  of  a  neighboring  kingdom,  one  of  our  most  cele¬ 
brated  astronomers  hastened  across  the  channel,  and  while 
others  were  chaffering  with  its  possessor  about  the  price,  our 
countryman  stept  in,  and  paying  at  once  the  full  amount  de¬ 
manded,  brought  off  the  prize,  to  the  great  mortification  of  his 
competitors. 


CHAP.  xn. 

ON  THE  SPECIFIC  GRAVITY  OF  GLASS. 

Importance  of  this  duality. — Experiments  of  Loysel. — His  Reasonings  and 
Formulae. — Specific  weight  augmented  by  Lime. — Mixed  Glasses. — Their 
Specific  weight. — Method  of  Determining  this. — Influence  ofTemperature 
on  the  Specific  weight  of  Glass. 

The  specific  gravity  of  glass  is  a  quality  of  considerable  im¬ 
portance,  when  the  material  is  required  for  conversion  into  the 
object-glasses  of  achromatic  telescopes,  or  for  the  composition 
of  counterfeit  gems,  although  any  very  minute  attention  to  this 
point  is  not  considered  essential  in  conducting  the  commoner 
processes  of  the  glass-house. 

Loysel,  to  whose  justly  esteemed  work  on  the  art  of  glass¬ 
making  allusion  has  been  so  frequently  made  in  these  pages, 
went  through  a  series  of  experiments  upon  the  specific  gravi¬ 
ties  of  various  vitreous  bodies,  with  the  view  of  giving  such 
instructions  for  the  composition  of  the  nicer  qualities  of  glass, 


CHAP.  XII. 


SPECIFIC  GRAVITY  OF  GLASS. 


203 


as  should  absolve  manufacturers  from  the  necessity  of  making 
those  preliminary  trials  upon  every  occasion,  which  are  attended 
by  much  inconvenient  delay  in  the  prosecution  of  extensive 
operations. 

Adopting  the  practical  aim  of  this  French  author,  some  of 
his  ingenious  formula;  will  be  here  given,  together  with  a  state* 
rnent  of  the  premises  whereupon  they  wTere  founded. 

The  specific  gravity  of  water  being  expressed  by  the  num¬ 
ber  100,  that  of  sand  is  263;  while  soda  deprived  of  all  car¬ 
bonic  acid  by  fusion  in  the  furnace  of  a  glass-house,  is  of  the 
specific  weight  199,  and  the  same  substance,  when  brought 
again  by  cooling  to  a  concrete  state,  is  not  heavier  than  222. 
It  might,  therefore,  be  supposed  that  the  specific  weight  of 
glass,  considered  as  a  compound  of  sand  and  alkali,  would  be 
diminished  in  proportion  as  its  dose  of  silica  was  lessened  and 
that  of  its  alkali  was  augmented.  The  contrary  of  this  fact 
results,  however,  from  the  combination  of  these  two  substances 
through  the  agency  of  fire. 

“  Sand,”  says  M.  Loysel,  “  contains,  in  addition  to  silica, 
some  other  substance,  the  nature  of  which  has  not  been  investi¬ 
gated,  and  which  is  sensibly  disengaged  from  the  silica  by  the 
alkali,  in  the  form  of  an  elastic  fluid,  in  the  act  of  their  com¬ 
bination  to  form  glass. 

“We  are  ignorant  of  the  degree  wherein  caloric  adheres 
more  or  less  strongly  to  one  or  other  of  these  substances ;  in 
other  words,  their  capacity  for  heat  is  not  known ;  but,  in 
order  to  avoid  errors,  it  will  suffice,  that  we  know  the  results 
of  several  similar  combinations.  If  we  ascertain  carefully  the 
doses  of  silica  and  alkali,  which  compose  glasses  formed  of 
these  substances  at  different  degrees  of  heat,  together  with 
their  various  specific  gravities,  we  perceive  that  the  differences 
between  their  doses  of  alkali  are  obviously  proportional  to  the 
differences  of  their  weights.  Knowing  then  how  far  these 
proportions  vary  in  respect  of  two  descriptions  of  glass,  we 
have  it  in  our  power  to  compute,  with  respect  to  a  third  com¬ 
position,  either  its  quantity  of  alkali  from  its  specific  gravity, 
or,  on  the  other  hand,  its  weight  from  its  dose  of  alkali.” 

From  actual  experiments  made  on  different  glasses,  the  fol¬ 
lowing  results  have  been  obtained,  the  weight  of  water  being 
expressed  by  100  : — 

Glass,  No.  1.  contained  80  parts  silica,  20  parts  alkali,  its  specific  gravity  236 
No.  2  — —  54  —  silica,  46  —  alkali,  its  specific  gravity  254 


Difference 


26 


18 


If  it  be  then  required  to  know  what  proportions  of  the  same 
materials  must  be  used  for  the  production  of  another  glass, 


204  GLASS  MANUFACTURE.  CIIAr.  XII. 

No.  3.,  the  specific  gravity  of  which  will  be  242,  the  solution 
of  the  question  may  be  found  by  the  following  formulae : — As 
the  difference  between  the  specific  weights  of  the  compounds  1. 
and  2.,  which  is  18,  is  to  the  difference  between  the  weights 
of  1.  and  3.,  which  is  6  :  so  is  the  difference  between  the  doses 
of  alkali  employed  in  Nos.  L  and  2.,  which  is  26,  to  the  differ¬ 
ence  between  the  doses  of  Nos.  1.  and  3.,  and  which  difference 
is  thus  found  to  be  9.  Adding  then  this  number  to  that  which 
represents  the  alkali  of  No.  1.,  we  may  conclude  that  the  glass 
of  No.  3.  must  contain  29  parts  of  alkali  and  71  parts  of  silica. 
It  has  been  proved  by  experiment  that  glass  of  the  specific 
gravity  proposed,  242,  is  composed  by  the  union  of  70  of  silica 
with  30  of  alkali. 

When  a  manufacturer  has  thus  two  well-established  results 
to  serve  as  general  means  of  comparison,  the  simple  ascertain¬ 
ment  of  specific  gravities  will  suffice  for  determining  if  any 
variation  lias  taken  place  in  the  manufacture,  as  well  as  for 
discovering,  and  in  general  remedying,  its  cause. 

If  any  lime  enters  into  its  composition,  as  is  the  case  with 
glass  of  common  quality,  its  weight  is  rapidly  augmented,  and 
it  is  therefore  useful  to  determine,  from  time  to  time,  the 
weight  of  the  glass  produced,  comparing  it  with  that  of  some 
other  sample  which  is  known  to  have  been  well  and  carefully 
made.  If  it  is  seen  that  the  weight  increases,  it  may  be  con¬ 
cluded,  either  that  a  larger  proportion  than  usual  of  lime  is 
present,  or  that  the  fire  has  not  been  sufficienty  urged,  and  that 
too  large  a  proportion  of  alkali  has  been  allowed  to  remain  in 
combination  with  the  glass. 

The  rule  already  stated  is  said  by  M.  Loysel  to  apply  with 
equal  certainty  to  the  heavy  glasses  composed  of  silica  and 
oxide  of  lead,  the  differences  between  the  weights  of  various 
specimens  of  flint-glass  being  also  proportional  to  the  differ¬ 
ences  in  their  quantities  of  metallic  oxide  : — 

Glass,  No.  1.  composed  of  27  sand  73  minium,  has  a  specific  gravity  of  520 


No.  2.  - -  11  —  89  -  -  657 

Difference . 16  137 


From  these  data,  the  specific  gravity  of  another  composition, 
No.  3. — made  up  of  20  parts  sand  and  80  parts  minium,  may 
thus  be  ascertained  : — As  the  difference  between  the  quantities 
of  minium  contained  in  Nos.  1.  and  2.  is  to  the  difference  be¬ 
tween  the  proportional  quantities  of  minium  in  Nos.  1.  and  3. ;  ; 
so  is  the  difference  between  the  weights  of  1.  and  2.  to  the 
difference  between  the  specific  gravities  of  1.  and  ? ,  and  which 
is  thus  found  to  amount  to  59  ;  which  number,  the  quantity  of 


CHAP.  XII.  SPECIFIC  GRAVITY  OF  GLASS.  205 

oxide  being  greater  in  No.  3.,  must  be  added  to  520,  the  weight 
of  No.  1.,  and  we  thus  have  579  as  the  weight  of  the  proposed 
composition. 

In  forming  flint  glass,  it  is  proper,  in  addition  to  the  sand 
and  minium  above  supposed,  to  employ  alkaline  substances ; 
and  it  is  desirable  that  the  manufacturer  should  have  it  in  his 
power  to  predict,  within  a  trifling  amount,  the  specific  weight 
of  every  compound  that  he  may  determine  to  employ.  The 
means  to  be  employed  by  him  for  the  attainment  of  this  end 
are  founded  on  the  following  considerations : — 

The  manufacture  of  flint  glass  requires  the  employment  of  a 
lower  degree  of  heat  than  is  necessary  for  the  formation  of 
other  descriptions,  which  do  not  contain  an  equal  abundance 
of  fluxing  materials  for  vitrifying  the  sand.  The  temperature 
of  the  furnace  is  commonly  such,  that  if  glass  be  made  in  it 
composed  of  silica  and  alkali  in  such  proportions  that  the  one 
will  saturate  the  other,  it  will  usually  contain  about  75  parts 
of  silica,  and  25  parts  of  alkali ;  and  this  glass  will  have  a  spe¬ 
cific  gravity  of  about  24.  The  same  means  of  heating  being 
employed,  73  parts  of  minium  will  be  saturated  by  27  parts  of 
sand,  producing  glass  the  specific  weight  of  which  is  52.  In 
practice,  it  is,  however,  probable,  that  75  parts  of  minium  will 
combine  with  25  of  sand,  and  the  result  will  have  the  specific 
gravity  of  54. 

On  the  other  hand,  if  two  glasses  of  different  character,  one 
of  which  is  composed  of  silica  and  alkali,  and  the  other  of  silica 
and  lead,  are  melted  together,  the  specific  gravity  of  each  being 
known,  the  weight  of  the  compound  resulting  from  their  union 
will  depart  in  only  a  very  trifling  degree  from  that  which 
would  be  given  by  calculation,  according  to  the  usual  rules  for 
determining  the  specific  gravities  of  alloys.  The  same  result 
will  equally  ensue,  if,  instead  of  thus  previously  forming  two 
different  kinds  of  glass,  the  materials  of  which  they  should  be 
composed  are  themselves  brought  together  for  the  purpose  of 
their  original  vitrification. 

If,  then,  we  consider  the  sand  of  the  composition  as  divided 
into  two  portions,  one  of  which  must  necessarily  combine  with 
the  minium  for  its  vitrification,  while  the  other  is  required  for 
the  saturation  of  the  alkali — the  surplus  quantity,  if  any,  of  the 
latter  constituent  being  dissipated  by  heat  during  the  process 
of  vitrification,  the  calculation  necessary  for  determining  the 
weight  of  the  compound  will  proceed  according  to  the  follow¬ 
ing  example: — 

Let  it  be  supposed  that  the  manufacturer  wishes  to  form  flint 
glass  by  the  union  of  100  parts  of  sand,  50  parts  of  minium, 
and  40  of  potash.  These  materials  might  be  divided  into  the 

S 


206 


GLASS  MANUFACTURE. 


CHAP.  XII. 


following  proportions  for  producing  two  very  different  descrip¬ 
tions  of  glass: — Thus,  the  50  parts  of  minium,  which  would 
be  reduced  in  the  process  of  vitrification  to  48  parts,  would  be 
completely  vitrified  by  the  addition  of  16  parts  of  sand  ;  the  ab¬ 
solute  weight  of  glass  thus  formed  would  be  64,  and  its  specific 
weight  (that  of  water  being  10)  would,  as  before  stated,  be  54. 
The  quantity  of  sand  remaining  (84  parts)  might  be  combined 
with  the  whole  of  the  potash ;  but  as,  in  the  process  of  vitrifi¬ 
cation,  all  the  surplus  quantity  of  the  alkali  would  be  dissi¬ 
pated,  glass  would  be  formed  containing  84  parts  of  sand  and  28 
of  potash,  having  112  as  its  absolute,  and  24  as  its  specific 
weight.  If,  then,  the  whole  materials  are  placed  together  in 
the  crucible  for  their  original  vitrification,  we  shall  have,  after 
the  reduction  of  the  minium  by  2  parts,  and  the  dissipation  by 
heat  of  12  parts  of  potash,  a  glass,  the  absolute  weight  of 
which  is  176,  and  whereof  we  desire  to  know  the  specific 
gravity.  For  ascertaining  this,  the  specific  weights  of  the  two 
kinds  of  glass  that  might  be  separately  formed,  must  be  multi¬ 
plied  into  each  other,  and  their  sum  again  multiplied  by  the  ab¬ 
solute  weight  of  both,  in  order  to  find  a  dividend.  Proceeding, 
then,  with  the  absolute  weights  of  the  two  descriptions  of 
glass  which  might  be  formed,  and  multiplying  each  separately 
by  the  specific  weight  of  the  other,  adding  the  two  products 
together,  another  sum  will  be  obtained,  by  employing  which  as 
a  divisor,  the  quotient  will  be  equal  to  the  specific  gravity  of 
the  compound. 

Thus,  in  the  above  example,  the  specific  weights,  54  and  24, 
of  the  two  descriptions,  being  multiplied  into  each  other,  and 
their  sum  multiplied  by  176,  the  absolute  weight  of  both,  a 
product  will  be  obtained  of  228,096  for  the  dividend.  Multi¬ 
plying,  then,  64,  the  absolute  weight  of  one  glass,  by  24,  the 
specific  weight  of  the  other;  and  again,  112,  the  absolute 
weight  of  the  remaining  glass,  by  the  remaining  specific  weight 
54,  we  have  two  sums,  1536  and  6048,  which,  added  together, 
and  employed  as  a  divisor,  gives,  as  its  quotient,  a  very  minute 
fraction  over  30,  which  is  known  to  be  the  specific  gravity  of 
glass  composed  of  sand,  minium,  and  potash,  in  the  proportions 
first  stated. 

With  respect  to  heavy  glasses,  results  are  obtained  by  calcu¬ 
lation,  which  are  rather  greater  than  the  reality ;  a  circum¬ 
stance  for  which  it  is  not  difficult  to  account  The  great  abun¬ 
dance  of  oxide  of  lead  used  in  their  composition,  attacks  the 
body  of  the  crucible,  so  as  partially  to  dissolve  it ;  and  being 
thus  provided  with  a  somewhat  larger  proportion  of  the  lighter 
material,  the  weight  of  the  compound  will  be  necessarily  and 
proportionally  diminished.  This  difference  between  the  com- 


CHAP.  XII. 


SPECIFIC  GRAVITY  OF  GLASS. 


207 


puted  and  the  real  weights  will,  of  course,  be  greater,  according 
as  the  proportion  of  minium  is  augmented ;  its  action  upon  the 
crucible  being,  by  such  means,  rendered  more  destructive. 

Notwithstanding  the  degree  of  uncertainty  thus  occasioned, 
it  must  still  be  useful  to  know  how,  by  a  very  simple  calcula¬ 
tion,  to  make  a  near  approximation  to  the  truth,  and  thus,  as 
already  said,  to  avoid  the  necessity  of  conducting  long  and  un¬ 
certain  preliminary  experiments. 

The  specific  gravity  of  glass  is  influenced  by  the  degree  of 
heat  to  which  it  has  been  exposed  during  its  vitrification;  be¬ 
ing  always  least  when  the  temperature  has  been  greatest.  The 
cause  of  this  variation  is  to  be  found  in  the  different  quantities 
of  alkali  that  have  been  dissipated,  the  silica  appearing  to  de¬ 
part  from  the  completeness  of  its  aggregation,  in  proportion  as 
it  is  deprived  of  alkali.* 

Flint  glass  is  not  entitled  to  any  drawback  upon  its  exporta¬ 
tion,  unless  its  specific  gravity  be  at  least  three  times  that  of 
water.  The  duty  drawn  back  on  the  shipment  of  flint  glass  is 
considerably  greater  than  the  rate  originally  paid  on  other  de¬ 
scriptions  ;  and  but  for  the  resort  which  is  had  to  its  gravity  as 
a  test,  those  other  descriptions  might  in  many  cases  be  substi¬ 
tuted,  and  a  considerable  profit  be  thereby  fraudulently  obtain¬ 
ed  by  the  exporter  at  the  expense  of  the  revenue. 


*  The  rule  for  ascertaining  the  mean  specific  gravity  of  different  bodies 
should  never  be  relied  on  until  verified  by  experiment.  The  condensation  of 
volume  which  some  substances  undergo  when  brought  into  combination 
with  others,  is  such  as  to  render  all  calculations  concerning  them,  under 
such  circumstances,  vague  and  erroneous.  From  the  experiments  of  M. 
Loysel  it  would  appear,  however,  that  except  in  the  case  which  he  has  no¬ 
ticed,  that  of  employing  different  degrees  of  heat,  this  condensation  does  not 
occur  with  the  various  compositions  of  which  glass  is  formed,  and  recourse 
may  therefore  be  had  to  the  formula  usually  employed  for  ascertaining  mean 
specific  gravities,  when  we  desire  to  determine  those  of  different  vitreous 
combinations.  The  rule  is  as  follows : 

The  specific  gravity  of  one  body  is  to  that  of  another,  as  the  weight  of 
the  first  divided  by  its  volume  is  to  the  weight  of  the  second  divided  by  its 
volume  ;  and  the  mean  specific  gravity  of  the  two  is  found  by  dividing  the 
sum  of  the  weights  by  the  sum  of  the  volumes. 

Let  W,  to,  be  the  two  weights ;  V,  v,  the  two  volumes ;  P,  p ,  the  two  spe¬ 
cific  gravities  ;  and  M,  the  calculated  mean  specific  gravity. 

W  -\-W  W  id  W p  -f-  w>P 

Then,  M  =  - - ;  andV  -{-  v= - 1 - = - ;  hence 

V  +  tJ  P  p  P p 

W  -f  w  W  -}-  w  (W  -f-  w)  P p 

-  —  -  —  - ; -  =  M. 

V-f»  W p  4-  w¥  Pto  -(-  pW 


208 


GLA6S  MANUFACTURE. 


CHAP.  XIII. 


CHAP.  Xffl. 

ON  THE  ART  OF  COLORING  GLASS. 

Antiauity  of  this  Art. — Specimens  of  Roman  Mosaic. — Analysis  of  these 
by  Klaproth— Metallic  Oxides.— Gold-Purple.— Its  great  Coloring  Power. 
— Kunckel. — His  Proficiency  in  Coloring  Glass. — Yellow  Color — From  Sil¬ 
ver — From  Lead — From  Tartar — From  Beechwood  Charcoal — From  Oxide 
of  Iron.— Green.— Black  Glass.— Blue.— Directions  found  in  old  Authors. 
— Imitation  of  the  Garnet — Of  the  Amethyst — Of  the  Emerald — Of  Sap¬ 
phires. — Opaque  Glasses — Black — White — Opal. — Ancient  Pictures  form¬ 
ed  of  Colored  Glass — How  executed. — Description  of  Ancient  Mosaics. — 
More  recent  Prosecution  of  this  Art. — Accidental  Coloring  of  Plate  Glass 
at  St.  Gobain. — Ineffectual  Attempts  to  reproduce  this  Effect. 

It  appears  probable  that  the  art  of  coloring1  glass  was  disco¬ 
vered  and  prosecuted  at  a  period  very  little  subsequent  to  that 
of  the  manufacture  of  the  article  itself.  The  most  ancient  au¬ 
thors  who  have  mentioned  the  existence  of  the  material,  have 
also  recorded  the  fact  of  its  being  tinged  with  various  colors, 
in  imitation  of  gems.  Strabo,  Seneca,  and  Pliny,  all  make 
mention  of  this  use,  as  being  one  to  which  glass  was  applied 
by  artists  in  very  early  times. 

The  fact  has  already  been  mentioned  of  colored  figures  hav¬ 
ing  been  found  with  Egyptian  mummies,  and  which  are,  there¬ 
fore,  known  to  have  been  in  existence  for  upwards  of  3000 
years.  These  curious  relics  of  ancient  times  have  also  been 
discovered  decorated  with  colored  glass  beads ;  and  a  mummy 
thus  ornamented  is  to  be  seen  in  the  British  Museum. 

In  the  reign  of  Augustus,  the  Romans  began  the  use  of  co¬ 
lored  glass  in  the  composition  of  mosaic  decorations.  Several 
specimens  of  this  kind  have  been  found  at  a  late  period,  among 
the  ruins  of  a  villa  built  by  Tiberius  in  the  island  of  Capri ; 
and  some  of  these  specimens  having  been  subjected  to  analysis 
by  the  accurate  and  ingenious  Klaproth,  it  is  known  that  in 
that  early  time  recourse  was  had  to  the  same  class  of  coloring 
ingredients  as  is  employed  by  the  moderns.  Some  difference 
must,  indeed,  have  been  observed  in  their  processes,  as  the  an¬ 
cients  were  unacquainted  with  the  use  of  the  mineral  acids, 
which  are  now  found  to  be  so  convenient  in  the  preparation  of 
metallic  oxides. 

Klaproth  has  given  the  following  as  the  result  of  his  exami¬ 
nation  of  some  of  the  Roman  specimens  above  mentioned : — 

One  which  was  a  lively  copper  red,  opaque,  and  very  bright 
where  recently  fractured,  contained,  in  200  grains, — 


CHAP.  XIII. 


COLORING  OF  GLASS. 


209 


SiJex . 142 

Oxide  of  lead .  28 

copper .  15 

iron .  2 

A1  amine .  5 

Lime .  3 


195 


Another,  a  light  verdigris  green,  also  opaque,  with  a  splendent 
fracture  and  scoriaceous,  contained  in  a  similar  quantity, — 


Silex . 130 

Oxide  of  copper .  20 

lead .  15 

iron .  7 

Lime .  13 

Alumine .  11 


196 


It  is  remarkable  that  the  constituent  ingredients  of  both  these 
specimens  should  prove  to  be  the  same.  The  difference  be¬ 
tween  them  exists  only  in  their  relative  proportions ;  and  the 
colors  depend  upon  the  different  degrees  of  oxidation  off  the 
copper.  Sub-oxide  of  copper, — that  is,  copper  which  has  com¬ 
bined  with  itself  only  half  the  quantity  of  oxygen  required  for 
the  production  of  the  perfect  oxide — produces  a  red  enamel ; 
while  that  which  has  received  its  full  proportion  of  oxygen 
yields  a  green  enamel  color. 

The  specimen  of  ancient  blue  glass  which  was  analyzed  by 
Klaproth  contained, — 


Silex . 163  parts. 

Oxide  of  iron .  19 

copper . .  1 

Alumine .  3 

Lime .  0* 


186* 


It  appears,  therefore,  to  have  been  indebted  to  the  oxide  of  iron 
for  its  blue  color,  as  no  trace  was  detected  of  any  other  ingre¬ 
dient  to  which  this  could  be  referred.  Since  the  discovery  of 
the  certain  and  commodious  method  of  producing  blue  enamel 
by  means  of  cobalt,  the  art  of  obtaining  this  color  from  iron  has 
been  lost. 


210 


GLASS  MANUFACTURE. 


CHAP.  XIII. 


The  causes  which  influence  the  employment  of  metallic  ox¬ 
ides  for  the  embellishment  of  porcelain  have  been  sufficiently 
detailed  in  the  preceding  treatise.  The  same  reasons  also 
oblige  the  artist  to  have  recourse  to  the  same  class  of  sub¬ 
stances  for  imparting  colors  to  glass.  The  mode  of  application 
of  coloring  materials  to  these  two  branches  of  manufacture  dif¬ 
fers,  however,  in  this, — that  while,  in  ornamenting  porcelain, 
they  are  applied  superficially,  in  the  manner  of  pigments,  they 
enter  more  intimately  into  the  composition  of  glass,  being 
transfused  through  the  whole  mass,  and  equally  incorporated 
with  its  entire  substance. 

The  preparation  of  metallic  oxides  as  coloring  materials  is 
nearly  similar  in  all  cases ;  it  will  not,  therefore,  be  necessary 
here  to  repeat  directions,  or  to  give  many  explanations  upon 
that  head. 

Gold,  in  a  state  of  great  division  and  oxidated,  has  long  been 
celebrated  as  a  means  for  imparting  to  glass  a  most  exquisite 
purple-red  color  resembling  the  ruby,  and  nearly  equalling  that 
gem  in  the  richness  of  its  hue.  It  is  not  by  any  means  easy  to 
prepare  glass  of  this  color  with  any  certainty  of  a  successful 
result.  The  great  tendency  which  is  shown  by  gold  to  assume 
the  reguline  state,  when  exposed  to  excessive  heat,  to  carbona¬ 
ceous  vapors,  or  to  the  action  of  hydrogen,  renders  necessary  a 
great  degree  of  careful  management  in  the  various  processes. 

The  manner  has  already  been  given  of  preparing  the  purple 
precipitate  of  Cassius ;  the  form  wherein  gold  has  been  used 
with  so  much  celebrity  in  imparting  red  and  purple  colors.  It 
lias  been  very  generally  imagined,  that  the  tin  used  in  the  pre¬ 
paration  of  this  precipitate  is  essential  to  the  production  of  the 
requisite  color ;  an  opinion  which  has  been  shown  to  be  void  of 
foundation,  as  preparations  of  gold  have  been  made  without  the 
agency  of  tin,  and  which  have  equally  possessed  the  power  of 
imparting  the  finest  purple  color  to  glass.  The  coloring  proper¬ 
ty  of  any  of  the  simple  oxides  of  gold  is  found  to  be  mate¬ 
rially  greater  than  that  of  Cassius’s  precipitate ;  which  circum¬ 
stance  has  been  brought  forward  as  another  argument  to  prove 
that  the  presence  of  tin  is  far  from  adding  any  thing  to  the 
body  of  the  color.  It  is  probable,  however,  that,  although  not 
indispensable,  tin  is  yet  useful,  as  enabling  the  gold  to  bear 
without  reduction  a  higher  degree  and  a  longer  continuance  of 
heat.  With  this  same  object,  it  has  been  recommended  to  add 
to  the  precipitate,  before  using  it,  a  small  quantity  of  nitre,  by 
which  the  gold  will  be  preserved  at  its  due  degree  of  oxidation. 

It  is  not  essential  that  gold  used  for  this  preparation  should 
be  absolutely  pure  or  unalloyed ;  since  neither  copper  nor  sil- 


CHAP.  XIII.  COLORING  OF  GLASS.  211 

ver,  when  present  in  small  quantities,  appears  to  alter  or  di¬ 
minish  its  coloring  power. 

Fulminating  gold,  prepared  by  precipitating  the  metal  from 
its  nitro-muriatic  solution  by  means  of  ammonia,  is  also  used  in 
coloring  glass ;  but  as  this  preparation  would  explode  violently 
when  exposed  to  a  heat  even  very  much  below  that  to  which 
it  must  be  subjected  in  use,  this  explosive  property  must  be 
previously  removed  by  mixing  it  with  a  fixed  alkali,  and  re¬ 
taining  it  for  some  time  at  a  comparatively  low  temperature. 
A  more  manageable  preparation  results  from  the  precipitation 
of  the  nitro-muriate  of  gold  by  means  of  carbonate  of  potash. 
This  is  not  fulminating,  as  it  is  from  the  presence  of  ammonia 
that  the  explosive  property  is  derived. 

A  very  ingenious  process  has  been  used  for  producing  an  in¬ 
timate  union  between  the  oxide  of  gold  and  silex.  This  con¬ 
sists  of  adding  to  the  solution  of  the  metal  in  nitro-muriatic 
acid,  a  proportion  of  silica  dissolved  in  an  alkaline  lixivium, 
and  pouring  therein  any  acid  in  sufficient  quantity  to  saturate 
the  alkali.  In  this  case,  the  silex  and  gold  are  precipitated  in 
very  intimate  combination ;  and  if  then  washed  with  clear 
water,  dried,  and  mixed  with  nitre,  borax,  or  any  other  suitable 
fluxing  substance,  will  be  fit  for  use  as  a  coloring  material. 

When  the  precipitate  of  Cassius  is  employed,  about  one 
sixth  part  of  its  weight  is  added  of  perfect  white  oxide  ot  anti¬ 
mony.  This,  from  imparting  a  yellowish  tinge,  is  considered 
to  be  an  important  ingredient  in  fine  ruby-colored  glass. 

The  proper  management  of  the  heat  employed  in  the  pro¬ 
duction  of  this  much-admired  preparation  is  a  difficult  acquire¬ 
ment,  known  only  to  clever  and  experienced  artists.  II  the 
temperature  be  allowed  to  rise  too  high,  the  color  will  be  much 
injured,  and  probably  even  altogether  destroyed.  The  contact 
of  every  kind  of  smoke  and  vapor  should  also  be  carefully 
avoided  in  the  fusion  of  ruby-colored  glass,  which  is  said  to  be 
apparently  colorless  when  it  leaves  the  crucible,  and  only  to 
put  on  its  exquisite  tint  as  it  becomes  cool. 

Kunckel  and  other  old  w’riters  upon  the  art  of  manufacturing 
glass  have  stated,  that  the  coloring  powers  of  the  purple  pre¬ 
cipitate  of  Cassius  are  so  considerable,  as  that  one  part,  if  added 
to  one  thousand  parts  of  glass,  will  impart  to  the  whole  a  full 
and  rich  body  of  color. 

The  artist  just  mentioned,  who  was  greatly  celebrated  for 
his  attainments  in  this  ornamental  branch  of  the  art,  was  in 
consequence  ennobled  by  Charles  XI.  king  of  Sweden,  and  as¬ 
sumed  the  name  of  Lowenstiern.  He  made  artificial  rubies, 
which  were  highly  esteemed,  and  which  he  sold,  in  the  man¬ 
ner  of  real  gems,  according  to  their  weight,  and  at  very  consid- 


GLASS  MANUFACTURE. 


CHAP.  XIII. 


212 

erable  prices.  The  achievement  upon  which  he  most  prided 
himself!  was  the  production  of  a  cup  of  ruby  glass,  which  was 
of  the  thickness  of  an  inch,  and  weighed  twenty-four  pounds : 
this  cup  went  into  the  possession  of  the  elector  of  Cologne. 

Kunckel  directed,  in  1679,  the  operations  of  the  glass-houses 
at  Potsdam,  where  he  met  with  the  greatest  encouragement, 
and  was  liberally  assisted  in  his  researches  by  the  elector  of 
Brandenburg,  who  expended  the  sum  of  1600  ducats  to  assist 
the  efforts  of  the  artist  towards  attaining  perfection  in  the  art 
of  making  ruby  glass.  A  cup,  with  a  cover  of  this  material, 
which  was  made  by  him,  and  is  still  in  existence  at  Berlin, 
continues  to  be  an  object  of  much  admiration. 

Silver,  in  all  its  forms  of  oxidation,  imparts  a  very  pure  and 
beautiful  yellow  color  to  vitreous  bodies;  but  this  color  is  easi¬ 
ly  destroyed,  through  the  accidental  employment  of  too  high  a 
degree  of  heat ;  an  evil  against  the  occurrence  of  which  it  is  so 
exceedingly  difficult  to  provide,  that  silver  is  very  seldom  re¬ 
sorted  to  as  a  coloring  material  by  glass-workers.  The  incon¬ 
venience  here  mentioned  may  in  some  degree  be  avoided 
when  oxides  of  silver  are  used  in  combination  with  alumirxe,  as 
in  the  ornamenting  of  porcelain ;  but  this  remedy  is  manifestly 
inapplicable  to  glass.  Other  bodies  can,  however,  be  used  with 
the  best  effect  in  imparting  a  yellow  color  to  this  substance. 

Oxide  of  lead  employed  alone,  if  in  very  considerable  quanti¬ 
ty,  would  give  a  very  good  yellow  color ;  but  as  it  would  re¬ 
quire  that  at  least  three  fourths  of  the  weight  of  the  glass 
should  be  made  up  of  this  oxide,  in  order  to  give  sufficient  in¬ 
tensity  to  the  color,  it  is  very  seldom  used  for  the  purpose. 
Glass  thus  formed  would  be  inconveniently  soft,  and  from  its 
powerful  fluxing  quality  would  act  injuriously  upon  the  cruci¬ 
bles  in  which  it  was  made. 

Chromate  of  lead,  which  is  not  liable  to  the  objections  just 
mentioned,  is  on  that  account  used  preferably.  Before  the  com¬ 
paratively  recent  discoveries  in  chemical  science  had  shown  to 
artists  in  what  manner  to  procure  this  valuable  coloring  ingre¬ 
dient  with  sufficient  facility  and  at  a  moderate  cost,  the  makers 
of  colored  glass  employed  the  oxides  of  lead,  silver,  and  anti¬ 
mony  in  combination,  for  the  production  of  yellow  colors ;  vary¬ 
ing  the  proportions  wherein  each  substance  was  used  according 
to  the  hue  which  it  was  desired  to  impart. 

Colors  varying  in  their  shades  from  brown  to  a  fine  transpa¬ 
rent  yellow  may  be  given  to  common  glass  by  simply  adding  to 
it,  while  in  a  state  of  perfect  fusion,  some  vegetable  carbonace¬ 
ous  matter.  This  must  always  be  supplied  in  excess,  since 
part  of  it,  rising  to  the  top  of  the  crucible,  will  be  burnt  away; 
but  some  portion  will  also  continue  uniformly  diffused  through- 


CHAP.  XIII.  COLORING  OF  GLASS.  213 

out  the  glass,  and,  without  at  all  impairing  its  transparent  qual¬ 
ity,  will  give  to  it  a  very  fine  yellow.  The  substance  which 
most  commonly  has  been  employed  for  this  purpose  is  tartar ; 
but  almost  any  solid  and  inflammable  vegetable  matter  will 
probably  answer  equally  well.  Charcoal  made  from  beechwood 
is  found  to  be  altogether  efficacious.  The  addition  of  a  small 
quantity  of  nitre  is  sometimes  useful  in  clearing  the  color  and 
removing  any  cloudiness  which  it  may  have  contracted ;  but  if 
great  discretion  be  not  shown  in  the  addition  of  this  substance, 
the  color  will  be  altogether  destroyed.  During  the  time  of  its 
preparation,  the  glass  swells  very  much  in  the  crucible,  owing 
to  the  escape  of  part  of  the  carbonaceous  matter  in  the  form  of 
gas ;  and  when  tartar  is  employed,  this  effect  is  experienced  in 
an  exaggerated  degree.  It  is  said  that  this  effervescence  might 
be  avoided,  if  freshly  burnt  and  perfectly  dried  charcoal  were 
heated  strongly  in  a  close  vessel,  and  added  in  that  state  to  the 
contents  of  the  crucible. 

The  oxides  of  iron  give  many  and  very  different  shades  of 
enamel  colors.  It  has  already  been  mentioned,  that  the  green 
color  of  common  bottle-glass  is  owing  to  the  presence  of  iron 
in  the  unpurified  sea-sand  and  ashes  of  which  it  is  composed. 
An  increased  quantity  of  this  oxide,  if  applied  to  glass  when  in 
a  state  of  perfect  vitrification,  will  give  a  yellow  color  to  the 
mass.  A  still  larger  quantity  will  impart  a  brownish  black  hue, 
which,  however,  appears  to  be  nothing  more  than  a  yellow  very 
highly  concentrated,  as  the  latter  color  may  be  again  produced 
by  simply  diluting  the  contents  of  the  crucible  with  an  addi¬ 
tional  quantity  of  uncolored  glass. 

The  red  color  which  is  imparted  by  the  oxides  of  iron  to  por¬ 
celain,  is  owing  to  its  state  of  imperfect  vitrification,  whereby 
the  metal  is  held  suspended  in  a  state  of  minute  division 
throughout  the  mass,  which  same  effect  is  indeed  apparent  in 
the  treatment  of  glass  up  to  a  certain  point ;  but  when  in  the 
advancing  stages  of  vitrification  the  heat  is  raised  so  that  a  per¬ 
fect  fusion  of  the  glassy  substance  as  well  as  of  the  oxide  is 
produced,  the  color  is  immediately  converted  to  yellow. 

The  use  of  the  black  oxide  of  manganese  in  correcting  the 
impurities  of  the  alkali  employed  in  the  original  composition  of 
glass,  as  well  as  in  removing  the  green  tinge  resulting  from 
the  presence  of  iron  in  the  sand,  has  already  been  explained. 
Where  these  imperfections  do  not  exist  in  the  original  ingre¬ 
dients,  if  manganese  be  added  to  the  glass,  it  will  impart  a  pur¬ 
plish  red  color.  This  oxide  also  forms  a  principal  constituent 
in  the  production  of  black  glasses:  it  is  most  commonly  used  in 
combination  with  nitre.  If  any  portion  of  arsenical  salts  should 
j  be  present  in  the  glass,  it  is  altogether  useless  to  attempt  the 


GLASS  MANUFACTURE. 


CHAP.  XIII. 


214 


employment  of  manganese  as  a  coloring  ingredient,  since  its 
efficacy  would  be  wholly  destroyed. 

All  the  simple  as  well  as  the  carbonated  oxides  of  copper,; 
when  perfectly  vitrified  in  conjunction  with  any  kind  of  glass 
or  fluxing  material,  will  yield  a  very  fine  green,  and  the  chan¬ 
ces  of  complete  success  in  the  attainment  of  this  are  greater 
than  attend  the  production  of  most  other  colors.  It  appears  to; 
be  nearly  a  matter  of  indifference  which  of  the  combinations  of 
copper  with  oxygen  are  employed  for  the  purpose.  The  pre¬ 
parations  most  usually  chosen  are  either  the  carbonated  oxide 
resulting  from  the  addition  of  sulphate  of  copper  to  some  car-j 
bonated  alkali,  or  that  which  is  known  as  the  as  ustum,  which 
is  copper  oxidated  and  calcined  simply  by  means  of  heat  and 
the  access  of  air. 

Copper  may  be  made  to  yield  a  carmine  red  color,  and  if  mix-! 
ed  with  iron,  a  full  deep  red,  by  adding  to  the  glass  with  which; 
it  has  already  been  combined  a  quantity  of  tartar.  This  addi-j 
tion  must  not  be  made  until  the  glass  is  in  a  state  of  perfect  fu-| 
sion,  and  the  mixture  should  be  worked  off  without  delay.  Itj 
should  be  mentioned  that  when  used  for  the  production  of  these 
colors,  the  oxide  of  copper  must  be  reduced  to  nearly  the  regu- 
line  state.  If  the  heat  is  continued  long  after  the  tartar  has 
been  added,  the  effect  will  be  lost,  and  the  green  color  re¬ 
stored. 

When  the  oxides  of  copper  and  iron  are  thus  united  for  de¬ 
veloping  a  full  deep  red  color,  the  iron  must  be  to  the  copper 
in  the  proportion  of  three  parts  to  one ;  and  according  as  this 
proportionate  difference  is  lessened,  so  will  the  color  be  found 
to  approach  to  the  carmine  tint. 

The  time  for  stirring  in  the  tartar  should  be  chosen  when 
the  melted  glass  appears  of  a  faint  greenish  yellow  ;  the  whole 
mass  will  then  immediately  swell  up  prodigiously ;  and  upon 
again  subsiding  will  appear,  as  before  stated,  of  a  clear  red  co¬ 
lor,  and  fit  for  being  immediately  used.  It  is  probable  that  char¬ 
coal  or  other  carbonaceous  matters  might  be  substituted  for  tar¬ 
tar  in  this  process  with  equal  success. 

Copper  in  a  state  of  oxidation  is  often  used  when  combiner 
with  the  oxides  of  manganese  and  iron  for  the  production  of 
black  glass. 

The  protoxide  of  chromium  may  be  used  for  producing  r 
green  color  in  glass,  with  as  much  advantage  as  attends  its  em¬ 
ployment  in  the  embellishment  of  porcelain,  that  substance  be¬ 
ing  capable  of  sustaining  without  injury  the  highest  heat  of  the 
crucible.  Chrome  is  the  natural  coloring  matter  of  the  preciou: 
emerald,  and  is  found  to  be  a  very  valuable  substance  in  the 
composition  of  artificial  gems. 


CHAP.  XIII. 


COLORING  OF  GLASS. 


215 


Oxide  of  cobalt  is  universally  employed  for  the  production  of 
blue  colors  in  vitrifiable  bodies.  The  fine  deep  shade  which  it 
imparts  is  unalterable  by  fire  of  any  degree  of  intensity,  and  suc¬ 
ceeds  equally  well  with  every  different  composition  of  glass. 

This  metallic  oxide  is  also  employed  towards  the  composition 
of  other  colors :  combined  with  the  oxides  of  lead  and  antimony, 
it  furnishes  a  green ;  and  if  mixed  with  those  of  manganese  and 
iron,  produces  a  very  fine  black. 

Neri,  Kunckel,  and  Fontanieu  have  left  in  their  writings 
many  recipes  for  the  preparation  of  artificial  gems  through  the 
employment  of  different  coloring  materials.  The  directions,  as 
given  in  the  works  of  these  authors,  differ  so  importantly  the  one 
from  the  other  as  regards  the  proportions  best  fitted  for  the 
composition  of  the  same  article,  that  we  are  forced  to  believe 
either  that  some  great  errors  have  been  committed  on  the  part 
of  their  subsequent  editors,  or  that  the  writers  themselves  were 
wanting  in  the  kind  and  degree  of  knowledge  to  which  they 
pretended,  and  which  were  required  to  fit  them  for  the  task 
they  undertook. 

.  A  few  of  these  recipes,  and  such  as  appear  most  free  from 
this  objection,  may  be  here  given. 

The  basis  of  each  of  these  compositions  is  most  frequently 
either  one  of  the  colorless  glasses  or  pastes  described  in  Chap¬ 
ter  VII.,  or  some  other  very  similar  vitreous  compound ;  but  it 
sometimes  happens  that  the  constituent  materials  of  the  glass, 
and  the  proportions  wherein  they  are  to  be  brought  together, 
are  indicated  as  well  as  the  coloring  substances. 

The  following  is  recommended  by  Neri,  as  furnishing  a  very 
excellent  imitation  of  the  garnet : — Rock  crystal  2  ounces,  min¬ 
ium  6  ounces,  manganese  16  grains,  zaffre  2  grains.  This  must 
be  a  very  inconvenient  composition,  both  on  account  of  the  ex¬ 
ceeding  softness  of  the  glass,  and  the  destructive  effect  it  would 
have  upon  the  crucible  during  the  time  of  its  preparation.  We 
learn  from  the  analysis  of  Berzelius,  that  the  coloring  matter 
of  the  “  precious  garnet,”  that  being  the  variety  which  it  is 
wished  thus  to  imitate,  consists  of  the  black  oxide  of  iron  and 
oxide  of  manganese.  A  more  modern  recipe  than  the  fore¬ 
going  for  the  successful  imitation  of  this  gem,  consists  of  purest 
white  glass  2  ounces,  glass  of  antimony  1  ounce,  Cassius’s  pre¬ 
cipitate  1  grain,  oxide  of  manganese  1  grain ;  which  composi¬ 
tion  is  free  from  the  objections  to  which  that  of  Neri  is  so  justly 
exposed. 

The  directions  of  Fontanieu  for  imitating  the  color  of  the 
amethyst  are,  that  to  24  ounces  of  the  glass  composed  according 
to  instructions  given  in  Chap.  VII.  under  the  number  5,  are  to 
be  added  half  an  ounce  of  the  oxide  of  manganese,  4  grains  of 


216 


MANUFACTURE  OF  GLASS. 


CHAP.  XIII. 


the  purple  precipitate  of  gold,  and  l|oz.  of  nitre,  but  it  is  im¬ 
possible  to  believe  that  the  recipe  of  Fontanieu  has  been  cor¬ 
rectly  given.  The  quantity  of  coloring  matter  here  indicated 
would  be  better  proportioned  to  24  pounds  of  glass,  than  to  the 
same  number  of  ounces  as  directed. 

Many,  and  greatly  varying  instructions  have  been  given  for 
imitating  the  emerald.  Fontanieu  recommends  160  parts  of 
any  glass  basis  which  contains  a  large  proportion  of  lead,  4  parts 
of  oxide  of  copper  prepared  by  simple  calcination,  and  y8th  of  a 
part  of  any  oxide  of  iron ;  which  last  ingredient  is  added  for 
the  purpose  of  giving  something  like  a  richness  of  tint,  and  for 
correcting  the  coldness  of  hue  that  would  result  from  the  em¬ 
ployment  of  the  oxide  of  copper  alone.  The  presence  of  lead  in 
the  glass  would  also  conduce  to  the  same  end. 

Another  rule  given  from  the  same  authority  directs  the  use 
of  576  parts  of  glass,  similarly  constituted  to  that  pointed  out  in 
the  last  receipt,  6  parts  of  the  same  oxide  of  copper,  and  only 
jijth  of  a  part  of  oxide  of  iron ;  thus  differing  from  the  former 
compound,  only  as  to  the  proportions  wherein  the  coloring  in¬ 
gredients  are  employed. 

A  third  receipt  for  the  attainment  of  the  same  object  is  very 
different  from  the  two  preceding.  It  recommends  the  employ¬ 
ment  of  200  parts  of  fine  sand,  400  parts  of  minium,  8  of  cal¬ 
cined  verdigris,  and  as  much  as  1  part  of  oxide  of  iron.  A  fourth 
method  for  the  composition  of  glass  of  an  emerald  green  is,  to 
mix,  in  due  proportions,  some  blue  glass  colored  by  means 
of  oxide  of  cobalt,  with  yellow  glass  prepared  with  oxide  of  an¬ 
timony.  A  great  many  other  prescriptions  are  offered  for  the 
imitations  of  emeralds,  but  these  vary  more  in  the  relative  pro¬ 
portions  of  their  ingredients  than  in  the  principle  of  their  com¬ 
position  ;  and  it  cannot,  therefore,  be  necessary  to  insert  them 
here. 

The  imitation  of  sapphires  is  always  effected  through  the 
coloring  agency  of  the  oxides  of  cobalt  and  manganese.  There 
is,  however,  a  material  difference  as  regards  tire  basis  of  the 
glass  in  the  various  directions  which  are  found  for  the  purpose ; 
one  recommending  that  this  shall  be  composed  without  lead, 
and  another  directing  that  this  mineral  shall  enter  largely  into 
the  composition  of  the  paste.  To  100  parts  of  glass  of  the  first 
kind  it  is  directed  that  1  part  of  zaffre,  and  y^th  of  a  part  of  ox¬ 
ide  of  manganese,  shall  be  added.  Where  the  second  descrip¬ 
tion  of  paste  is  recommended  as  the  basis,  the  artist  is  directed 
to  prepare  this  by  adding  to  240  parts  of  glass  frit  made  with 
only  soda  and  silica,  192  parts  of  minium,  2  of  zaffre,  and  jd  of 
a  part  of  manganese.  This  compound  must  be  fused  together, 


CHAP.  XIII.  COLORING  OF  GLASS.  217 

poured  into  water,  and  then  remelted  as  directed  by  Fontanieu, 
for  the  formation  of  the  pastes  described  in  Chapter  VII. 

The  oxide  of  cobalt  is,  in  the  present  day,  a  necessary  ingre¬ 
dient  in  every  imitation  of  the  sapphire,  so  that  it  is  never  at¬ 
tempted  to  act  without  it.  We  have  seen,  however,  that  a 
very  fine  blue  glass  was  formerly  made  having  the  oxide  of  iron 
for  its  coloring  ingredient,  and  as  it  is  known  that  the  coloring 
property  of  real  gems  having  that  hue,  resides  in  this  metal 
when  in  some  particular  state  of  oxidation,  we  must  own  to 
having  lost,  in  this  respect,  one  means  of  imitating  nature  which 
was  known  and  exercised  by  our  predecessors. 

The  colored  glasses  comprised  in  the  foregoing  descriptions, 
are  all  translucent.  The  preparation  of  others,  which  have  the 
opposite  quality  of  opacity,  is  effected  either  by  means  of  apply¬ 
ing  excessive  doses  of  the  same  metallic  oxides  which,  in  small¬ 
er  quantities,  are  used  for  imparting  colors ;  or  by  the  addition 
to  those  oxides  of  some  other  substance  which  has  the  property 
of  obstructing  the  rays  of  light  in  their  passage  through  the 
glass. 

In  general,  the  first  method  is  used  only  for  the  production 
of  black  glass,  while  the  second  plan  is  pursued  with  all  other 
descriptions,  as  well  those  which  are  designed  to  retain  a  per¬ 
manent  white  color,  as  with  yellow,  blue,  green,  or  any  other 
colored  opaque  glasses. 

The  most  approved  method  of  preparing  black  glass,  of  good 
quality,  which  shall  be  of  a  full  deep  black  and  perfectly  opaque, 
is  by  mixing  together  equal  parts  of  black  oxide  of  manganese, 
zaffre,  and  protoxide  of  iron  ;  adding  one  part  of  this  mixture  to 
fifteen  or  twenty  parts  of  colorless  transparent  glass,  and  fusing 
the  whole  together. 

Some  large  and  beautiful  slabs  of  perfectly  black  glass  have 
lately  been  imported  into  London  from  St.  Petersburgh,  and  ap¬ 
pear  well  fitted  to  be  used  as  substitutes  for  marble  in  the  con¬ 
struction  of  certain  articles  of  household  furniture. 

White  opaque  glass,  which  has  this  quality  imparted  to  it  by 
means  of  the  oxide  of  tin,  is  called  enamel ;  and  it  is  this  sub¬ 
stance  of  which  the  dial-plates  of  watches  and  of  table  clocks 
are  commonly  made.  This  compound  is,  however,  too  expen¬ 
sive  for  more  ordinary  uses,  and  a  very  good  white  glass  is  made 
for  such  purposes  by  substituting  for  the  oxide  of  tin,  a  consid¬ 
erable  proportion  of  phosphate  of  lime  in  the  state  of  a  very  fine 
powder.  This  substance  is  procurable  in  great  abundance,  and 
at  a  moderate  cost,  in  almost  every  situation.  Phosphate  of  lime 
is  extremely  infusible,  so  that  the  opaqueness  of  the  glass  with 
which  it  is  united,  arises  from  its  holding  in  intimate  mixture 
an  unvitrescible  earthy  salt. 


218 


GLASS  MANUFACTURE. 


CHAT.  XIII. 


One  receipt  given  by  Neri  for  producing  white  opaque  glass 
is  as  follows : — Mix  together  60  parts  of  fine  white  sand,  and  40 
parts  of  potash,  with  10  of  finely  pounded  bone-ash,  and  melt 
the  compound  during  the  same  length  of  time  as  is  usually  em¬ 
ployed  in  ordinary  glass-making.  It  is  said  that  this  glass  is 
transparent  for  as  long  as  it  continues  at  a  full  red  heat ;  and 
that,  as  it  gradually  cools,  it  first  puts  on  a  milky  appearance, 
and  afterwards  becomes  wholly  opaque.  If  this  change  does  in 
reality  take  place,  and  is  not  rather  the  result  of  a  deception 
which  prevents  the  proper  distinguishing  of  its  degree  of  opacity 
while  red-hot,  it  may  probably  arise  from  the  circumstance  that 
the  excessive  heat  of  the  melted  glass  enables  it  to  take  up  a 
greater  quantity — in  other  words — to  supersaturate  itself  with 
the  phosphate  of  lime,  which  it  parts  with  again  in  cooling. 

Another  receipt  of  the  same  artist  is  130  parts  of  calcined 
flint  or  fine  sand,  70  parts  of  nitre,  12  of  borax,  12  of  tartrate  of 
potash,  5  of  arsenic,  and  15  of  bone-ash. 

Fontanieu  has  given  directions  for  imitating  the  peculiar 
lustre  of  the  semi-transparent  opal,  by  mixing  576  parts  of  his 
glass  No.  3.  (Chap.  VII.,)  with  10  parts  of  muriate  of  silver,  2 
parts  of  magnetic  iron  ore,  and  26  parts  of  bone-ash.  The 
beautiful  play  of  colors  exhibited  by  the  “  precious  opal  ”  is  de¬ 
servedly  an  object  of  much  admiration,  and  it  has  always  been 
a  subject  of  interest  to  imitate  successfully  so  pleasing  an  effect 
Ornamental  pieces  of  opal  glass  have  usually  been  obtained 
from  France ;  but  their  production,  of  a  quality  fully  equal  to 
these  importations,  may  now  be  witnessed  in  the  London  glass¬ 
works. 

The  peculiar  delicacy  and  beauty  of  this  glass  do  not  appear 
while  it  remains  in  a.  state  of  fusion  or  at  a  red  heat,  and  are 
not  fully  developed  until  it  is  sufficiently  cooled  to  have  acquir¬ 
ed  its  quality  of  brittleness. 

Other  colored  glasses  which  are  opaque,  are  made  by  the 
same  processes  as  are  followed  with  transparent  glasses  of  the 
like  colors,  substituting  for  the  common  vitreous  base,  one  of  the 
above  described,  opaque-white  glasses. 

The  ancients  employed  methods  of  converting  colored  glasses 
into  representations  of  natural  objects,  which  were  extremely 
beautiful,  and  the  manner  of  producing  which  is  now  lost.  The 
existence  even  of  this  art  is  only  known  in  these  modern  days 
from  specimens  which  have  been  accidentally  discovered  ;  and 
our  knowledge  of  the  peculiar  nature  of  their  formation  is 
wholly  derived  from  the  examination  to  which  these  specimens 
have  been  subjected. 

The  first  mention  made  of  these  works  of  art  is  to  be  found 


CHAP.  XIII. 


COLORING  OF  GLASS. 


219 


in  the  Collection  of  Antiquities,”  by  count  Caylus,  who  de¬ 
scribed  them  as  composed  of  delicate  different-colored  fibres  of 
glass  joined  with  the  greatest  nicety,  and  conglutinated  into  a 
compact  homogeneous  mass  by  fusion.  Winkelmann,  in  his 
“  Annotations  on  the  History  of  the  Arts  among  the  Ancients,” 
describes  these  same  specimens  as  pictures  made  of  glass  tubes, 
and  introduces  them  to  further  observation  by  these  words : — 
“  The  works  of  the  ancients  in  glass  which  are  not  noticed  in 
the  history  of  the  arts,  deserve  particularly  to  be  mentioned  in 
this  place,  more  especially  because  the  ancients  carried  the  art 
of  working  in  glass  to  a  much  higher  degree  than  we  have  ar¬ 
rived  at ;  a  fact  which,  to  those  who  have  not  seen  their  works 
of  this  kind,  might  have  the  appearance  of  a  groundless  asser¬ 
tion.” 

The  author  just  quoted  particularly  describes  two  small 
pieces  of  glass  thus  constructed  which  were  brought  to  Rome 
in  the  year  1765,  and  which,  indeed,  appear  to  have  been  well 
deserving  of  his  careful  examination,  as  confirming  the  opinion 
he  had  given  respecting  the  superior  proficiency  of  the  an¬ 
cients.  The  account  of  these  curiosities  cannot  be  better  given 
than  in  Winkelmann’s  own  words: — “Each  of  them  is  not 
quite  one  inch  long,  and  one  third  of  an  inch  broad.  One  plate 
exhibits,  on  a  dark  ground  of  variegated  colors,  a  bird  repre¬ 
senting  a  duck  of  various  very  lively  colors,  more  suitable  to 
the  Chinese  arbitrary  taste,  than  adapted  to  show  the  true  tints 
of  nature.  The  outlines  are  well  decided  and  sharp ;  the  colors 
beautiful  and  pure,  and  have  a  very  striking  and  brilliant  effect, 
because  the  artist,  according  to  the  nature  of  the  parts,  has  in 
some  employed  an  opaque  and  in  others  a  transparent  glass. 
The  most  delicate  pencil  of  the  miniature  painter  could  not 
have  traced  more  accurately  and  distinctly  either  the  circle  of 
the  pupil  of  the  eye,  or  the  apparently  scaly  feathers  on  the 
breast  and  wings,  behind  the  beginning  of  which  this  piece  had 
been  broken.  But  the  admiration  of  the  beholder  is  at  the  high¬ 
est  pitch  when,  by  turning  the  glass,  he  sees  the  same  bird  on 
the  reverse,  without  perceiving  any  difference  in  the  smallest 
points ;  whence  we  could  not  but  conclude  that  this  picture  is 
continued  through  the  whole  thickness  of  the  specimen,  and 
that  if  the  glass  were  cut  transversely,  the  same  picture  of  the 
duck  would  be  found  repeated  in  the  several  slabs ;  a  conclu¬ 
sion  which  was  still  further  confirmed  by  the  transparent  places 
of  some  beautiful  colors  upon  the  eye  and  breast  that  were  ob¬ 
served.  The  painting  has  on  both  sides  a  granular  appearance, 
and  seems  to  have  been  formed  in  the  manner  of  mosaic  works, 
of  single  pieces,  but  so  accurately  united,  that  a  powerful  mag¬ 
nifying-glass  was  unable  to  discover  any  junctures.  This  cir- 


220 


GLASS  MANUFACTURE. 


CHAP.  XIII. 


cumstance,  and  the  continuation  of  the  picture  throughout  the 
whole  substance,  rendered  it  extremely  difficult  to  form  any 
direct  notion  of  the  process  or  manner  of  forming  such  a  work  ; 
and  the  conception  of  it  might  have  long  continued  enigmatical, 
were  it  not  that,  in  the  section  of  the  fracture  mentioned,  lines 
are  observable  of  the  same  colors  which  appear  on  the  upper 
surface  that  pervade  the  whole  mass  from  one  side  to  the  other ; 
whence  it  became  a  rational  conclusion,  that  this-  kind  of  paint¬ 
ing  must  have  been  executed  by  joining  variously  colored  fila¬ 
ments  of  glass,  and  subsequently  fusing  the  same  into  one  co¬ 
herent  body.  The  other  specimen  is  of  almost  the  same  size, 
and  made  in  the  same  manner.  It  exhibits  ornamental  draw¬ 
ings  of  green,  white,  and  yellow  colors,  which  are  traced  on  a 
blue  ground,  and  represent  volutes,  beads,  and  flowers,  resting 
on  pyramidally  converging  lines.  All  these  are  very  distinct 
and  separate,  but  so  extremely  small,  that  even  a  keen  eye 
finds  it  difficult  to  perceive  the  subtle  endings ;  those,  in  par¬ 
ticular,  in  which  the  volutes  terminate  ;  notwithstanding  which, 
these  ornaments  pass  uninterruptedly  through  the  whole  thick¬ 
ness  of  the  piece.” 

Klaproth,  who  had  in  his  possession  some  specimens  of  these 
antique  compositions  in  colored  glass,  compiled  a  paper  upon  the 
subject,  which  was  read  before  the  Royal  Academy  of  Sciences 
at  Berlin,  in  October,  1798 ;  and  the  collection  of  antiquities 
formed  by  Mr.  Townley,  comprised  a  ring  which  contained  a 
singular  antique  glass  paste,  which  represented  a  bird  of  so 
small  a  delineation,  as  not  to  be  distinctly  visible  without  the 
aid  of  a  magnifying  lens,  and  which  yet  had  every  appearance 
of  having  been  produced  in  the  manner  described  by  Winkel- 
mann.  Numerous  antique  specimens,  similarly  composed,  are 
deposited  in  the  British  Museum.  They  are  for  the  most  part 
fragments,  and  it  is  to  be  regretted  that  we  are  without  any 
records  of  their  origin. 

Keysler,  the  account  of  whose  travels  to  different  parts  of 
Europe  in  the  early  part  of  the  last  century  contains  a  great 
variety  of  entertaining  and  instructive  matter,  has  given  the 
following  description  of  a  mode  of  composing  pictures  in  col¬ 
ored  glass,  which  was  at  that  time  employed  in  decorating  some 
of  the  churches  in  Rome.  It  will  be  seen  that  the  methcxl  pur¬ 
sued  by  the  Roman  artists  in  some  respects  resembled  that  used 
for  the  composition  of  antique  pastes,  as  described  by  Winkel- 
mann.  Recourse  appears  to  have  been  had  to  this  mode  of  pro¬ 
ducing  pictures,  in  cases  where  the  original  paintings  on  wood 
or  canvas  were  perishing  through  the  dampness  of  the  walls, 
and  where  it  was  wished  to  supply  their  places  with  copies 
composed  of  an  imperishable  substance. 


CHAP.  XIII.  ROMAN  MOSAICS.  221 

“  The  materials  used  are  little  pieces  of  glass,  of  all  the  dif¬ 
ferent  shades  in  every  tint  or  color  like  those  of  the  fine  Eng¬ 
lish  worsted  used  in  needle-work.  The  glass  is  first  cast  into 
thin  cakes,  which  are  afterwards  cut  into  long  pieces  of  differ¬ 
ent  thickness.  Many  of  the  pieces  used  in  the  works  on  roofs 
and  ceilings,  which  are,  consequently,  seen  only  at  a  great  dis¬ 
tance,  appear  to  be  a  finger’s  breadth ;  but  the  finer  works  con¬ 
sist  only  of  glass  pins,  if  I  may  call  them  so,  not  thicker  than 
a  common  sewing-needle,  so  that  a  prtrait  of  four  feet  square 
shall  take  up  two  millions  of  such  pins  or  studs.  These  are  so 
closely  joined  together,  that,  after  the  piece  is  polished,  it  can 
hardly  be  discerned  to  be  glass,  but  rather  looks  like  a  picture 
painted  with  the  finest  colors.  The  ground  on  which  these 
vitreous  pieces  are  inlaid  is  a  paste  compounded  of  calcined 
marble,  fine  sand,  gum  tragacanth,  white  of  eggs,  and  oil :  it  is 
at  first  so  soft  that  the  pieces  are  easily  inserted,  and  upon  any 
oversight  may  be  taken  out  again,  and  the  paste  new  moulded 
for  the  admission  of  other  pins ;  but  by  degrees  it  grows  as  hard 
as  a  stone,  so  that  no  impression  can  be  made  on  the  work. 

“  This  paste  is  spread  within  a  wooden  frame,  which  for  the 
larger  pieces  must  not  be  less  than  a  foot  in  breadth  and  thick¬ 
ness.  A  piece  of  about  eighty  square  feet,  if  performed  with 
tolerable  care  and  delicacy,  will  employ  eight  artists  for  two 
years. 

“  The  pins  of  the  several  colors  lie  ready  before  the  artists 
in  cases,  as  the  letters  are  laid  before  the  compositors  in  a 
printing-house ;  and  such  is  their  accuracy  in  imitating  the 
finest  strokes  of  the  pencil,  that  the  only  apparent  difference 
betwixt  the  original  painting  and  such  a  copy  is,  that  the  latter 
has  a  much  finer  lustre,  and  the  colors  are  more  vivid.” 

An  accident  occurred  many  years  ago  in  the  plate-glass 
works  at  St.  Gobain,  which  seemed  to  offer  the  means  of  ob¬ 
taining  a  bright  red  color  for  glass  by  the  employment  of  cop¬ 
per,  at  a  much  less  expense  than  has  hitherto  attended  the  pro¬ 
duction  of  that  tint  from  gold. 

It  will  be  remembered  that,  in  the  manufacture  of  plate 
glass,  when  the  refining  is  completed,  and  it  is  wished  to  trans¬ 
fer  a  portion  of  its  contents  from  the  melting-pot  to  the  cu¬ 
vette,  a  copper  ladle  is  employed.  It  is  necessary,  while  using 
this  implement,  to  dip  it  occasionally  into  water,  lest  it  should 
become  too  hot  and  warp,  or  possibly  melt.  On  the  occasion 
referred  to,  the  workman  having  omitted  this  necessary  pre¬ 
caution,  the  last  of  these  misfortunes  ensued  ;  dipping  the 
heated  ladle  once  too  often  in  the  melted  glass,  only  part  was 
brought  out  attached  to  its  iron  handle. 

It  was  imagined  that  the  copper  thus  melted  would  sink,  by 

T  2 


222 


GLASS  MANUFACTURE. 


CHAP.  XIII. 


reason  of  its  greater  gravity,  to  the  bottom,  and  would  be  found 
there  in  the  metallic  state  on  the  emptying  of  the  pot  The 
casting  and  annealing  of  the  plates  were  proceeded  with  ac¬ 
cordingly  ;  and,  on  their  completion,  the  workmen  were  sur¬ 
prised  to  find  that  not  only  were  grains  of  metallic  copper  em¬ 
bedded  in  the  substance  of  the  glass,  but  bands  uniformly  col¬ 
ored  of  a  fine  bright  red  were  distributed  throughout  the  plates. 

The  color  must,  in  this  case,  have  been  produced  by  the  cop¬ 
per,  which  was  suddenly  carried  to  the  degree  of  oxidation 
necessary  for  its  development.  M.  Guyton-Morveau,  when  in¬ 
formed  of  this  circumstance,  was  desirous  of  ascertaining,  by 
direct  experiment,  what  means  would  be  most  efficacious  in 
producing  the  same  effect.  The  result  of  his  endeavors  has 
been  published.* 

The  first  attempt  was  made  -with  plate  glass.  In  order  to 
bring  the  glass  and  copper  into  more  intimate  union,  the  first 
was  reduced  to  powder,  and  the  other  was  used  in  the  form  of 
filings.  The  metal  was  used  in  the  proportion  of  3  parts  to 
100  parts  of  glass :  this  mixture  was  brought  to  a  state  of  com¬ 
plete  fusion  before  the  glass  was  poured  out.  No  success  at¬ 
tended  this  experiment,  the  glass  appearing  uncolored,  and  the 
copper  remaining  mixed  with  it  mechanically  in  the  form  of 
metallic  globules. 

The  next  trial  was  made  with  common  white  glass,  mixed 
with  twice  the  proportional  weight  of  copper  filings  that  had 
been  employed  in  the  first  experiment.  The  compound  having 
been  completely  melted,  was  found  to  have  assumed  a  red  color, 
which  was  uniformly  diffused  throughout  the  mass;  but  this 
color  was  so  deep  as  to  render  the  glass  nearly  opaque. 

A  trial  made  with  copper,  already  in  the  form  of  an  oxide, 
imparted  a  greenish  color  to  the  glass. 

It  is  impossible  not  to  remark  that  the  circumstances  under 
which  these  experiments  were  conducted,  as  detailed  by  M. 
Guyton-Morveau,  differ  in  some  essential  particulars  from  those 
which  accompanied  the  accident  by  which  they  were  suggested. 
In  that  case,  the  glass  was  already  in  the  state  of  fusion,  and 
probably  also  in  a  high  state  of  incandescence,  before  the  addi¬ 
tion  of  the  copper.  The  proportion  of  metal  used  in  the  second 
experiment  was  evidently  excessive ;  and  it  is  surprising  that 
t  he  effect  produced  did  not  lead  M.  Guyton-Morveau  to  try  the 
effect  of  a  smaller  proportion. 

Attempts  have  been  made  to  color  glass  by  subjecting  it  to 
the  action  of  heat,  while  surrounded  by  some  cementing  sub¬ 
stances  already  impregnated  with  metallic  oxides  as  coloring  in- 


*  An.  de  Chim.  vol.  lxxiii.  p.  132. 


CHAP.  XIII. 


COLORING  OF  GLASS. 


223 


gredients.  In  most  of  these  cases  the  glass  remained  perfectly 
colorless,  unless  the  heat  had  been  carried  sufficiently  far  to  in¬ 
duce  devitrification ;  which  state,  as  it  renders  the  material 
opaque,  furnishes  sufficient  objection  to  the  use  of  this  method 
of  coloring.  Even  in  those  cases  where  transparency  is  not  re¬ 
quired,  the  same  effect  can  be  attained  by  easier  means,  and 
free  from  a  very  serious  inconvenience,  that  of  the  adhesion 
of  the  cementing  substance  to  the  glass.  Some  curious  facts 
connected  with  this  subject  will  be  detailed  in  the  concluding 
chapter  of  this  volume,  which  treats  of  the  devitrification  of 
glass. 


CHAP.  XIV. 

ON  THE  ART  OF  STAINING  AND  PAINTING  GLASS. 

This  Art  more  recent  than  that  of  Coloring. — Encouraged  by  the  Monks. — 
Early  Specimen  at  St.  Denis. — Art  never  much  cultivated  in  England. — 
Splendid  Paintings  at  Gouda. — Directions  given  by  old  Authors  for  com¬ 
posing  Colors. — Fluxes. — Vehicles  for  diluting  Colors. — Description  of  va¬ 
rious  Stains. — Method  of  floating  these. — Of  painting  on  Glass. — Imitation 
of  ground  Glass  with  transparent  Patterns. — Description  of  Kiln  employed. 
— Method  of  firing. — Second  and  third  firing. — Ancient  method  of  fixing 
different  colored  Glasses  on  each  other. 

The  invention  of  the  art  of  painting  on  and  staining  glass, 
although  probably  recent  as  compared  with  that  of  coloring  the 
body  of  the  metal  when  in  fusion,  is  yet  known  to  have  existed 
for  many  centuries. 

The  exact  period  of  its  adoption  is,  indeed,  involved  in  much 
obscurity  ;  and  it  can,  at  best,  be  regarded  as  only  a  reasonable 
conjecture,  which  assigns  its  principal  excellence,  if  not  its  ori¬ 
gin,  to  the  fostering  care  of  those  religious  communities  which, 
upon  the  breaking  up  of  the  great  western  empire  of  Rome, 
became,  and  for  so  long  a  period  thereafter  continued,  the  sole 
depositaries  of  learning  and  the  arts  in  Europe. 

Endowed  by  the  piety  or  superstition  of  their  unenlightened 
followers  with  revenues  far  beyond  their  personal  wants,  the 
clergy  of  that  time  expended  a  portion  of  their  superfluous  wealth 
in  the  construction  of  those  splendid  temples  which  attest  to  the 
present  day  the  architectural  skill  and  genius  of  their  founders, 
remaining  unsurpassed  and  almost  unrivalled  in  their  kind  as 
objects  of  admiration  through  a  great  portion  of  Europe.  The 
ministers  of  a  religion  which  addressed  itself  to  the  imagina¬ 
tions  and  the  feelings  of  its  votaries,  thdy  could  not,  perhaps, 
have  adopted  more  effectual  means  for  obtaining  and  perpetu¬ 
ating  their  influence  over  the  multitude.  Some  idea  of  the  ex- 


224 


GLASS  MANUFACTURE. 


CHAIN  XIV. 


tent  to  which  these  means  must  have  operated  may  be  formed 
by  every  one  who  recalls  to  mind  the  sensations  of  solemnity 
amounting  to  awe  wherewith  he  has  himself  been  struck  as  he 
has  stood  beneath  the  lofty  sculptured  arches  of  a  cathedral,  or 
walked  through  its  lengthened  aisles,  radiant  with  tints  glow¬ 
ing  through  emblazoned  windows. 

The  earliest  specimens  of  these  embellishments  differ  from 
those  of  more  recent  date  in  having  been  formed  of  small  pieces 
of  glass  colored  throughout  during  the  process  of  its  original 
manufacture,  and  which,  to  distinguish  it  from  glass  colored  or 
stained  by  the  methods  that  will  be  hereafter  described,  has 
been  called  by  artists  pot  metal.  Pieces  of  this,  cut  to  the  shapes 
required,  were  joined  together  in  the  manner  of  mosaic  by  the 
interposition  of  lead,  in  a  way  which  has  since  fallen  greatly 
into  disuse;  the  method  of  staining  and  burning  in  metallic 
colors  on  the  surface  of  the  glass  having  been  found  far  more 
beautiful,  admitting  of  greater  variety  of  tints,  as  well  as  of 
those  delicate  shadings  which  were  manifestly  unattainable  by 
even  the  most  laborious  composition  in  mosaic  work. 

Perhaps  the  oldest  existing  specimen  of  this  later-discovered 
art  of  painting  on  glass  is  to  be  seen  on  the  windows  of  the  ab¬ 
bey  of  St.  Denis,  whereon  were  recorded,  in  1194,  various 
events  which  occurred  during  the  first  crusade. 

This  art  has  never  flourished  to  any  great  degree  in  England, 
where  at  no  time  have  men  of  genius  been  much  encouraged  to 
apply  their  talents  to  its  advancement :  many  among  the  most 
admired  specimens  of  painted  glass  which  ornament  our  re¬ 
ligious  edifices,  are  the  productions  of  foreign  artists. 

The  great  church  at  Gouda,  in  Holland,  is  splendidly  embel¬ 
lished  with  painted  windows,  which,  about  the  year  1555,  were 
executed  by  various  artists,  the  most  celebrated  among  whom 
were  Dirk  and  Walter  Crabeth.  The  one  among  the  windows 
which  is  the  most  highly  esteemed  was  painted  by  the  first 
mentioned  of  these  two  brothers ;  and  Mr.  Hollis  mentions,  as 
evidence  of  the  value  placed  upon  this  work  of  art,  that  for  the 
lower  part  of  this  window, — about  twenty  feet  square, — Mr. 
Trevor,  some  time  English  resident  at  the  Hague,  had  in  vain 
offered  to  give  a  solid  plate  of  gold  of  the  same  surface,  and  of 
the  thickness  of  three  Dutch  guilders. 

This  particular  division  of  the  fine  arts  differs  from  other 
branches  in  containing  within  itself  fewer  incentives  to  its  pros¬ 
ecution.  Its  practice  is  accompanied  by  various  laborious  and 
differing  processes.  The  range  of  subjects  which  it  admits  is 
far  more  circumscribed,  and  the  opportunities  which  it  offers  for 
the  display  of  excellence  are  far  less  frequent.  The  artist  is 
even  without  the  gratification  of  witnessing  the  satisfactory 


CHAP.  XIV.  STAINING  AND  PAINTING  GLASS.  225 

progress  of  his  own  work,  the  appearance  of  which  is  compara¬ 
tively  dull  and  uninteresting  until  after  it  has  passed  from  his 
own  hands  into  those  of  “  red  Lemnos’  artisan.”  The  sculptor 
and  the  painter  in  oil  colors  can  seldom  fail  in  procuring  means 
for  exhibiting  their  works ;  so  that,  according  to  the  degree  of 
talent  evinced  by  them  will  generally  be  their  encouragement 
and  reward ;  while  the  man  who  has  conquered  every  disad¬ 
vantage  attending  the  processes  of  staining  glass,  and  who  may 
have  produced  a  piece,  the  conception  and  execution  of  which 
are  alike  honorable  to  his  genius  and  assiduity,  might  look  in 
vain  for  the  opportunity  of  bringing  its  merits  before  the  world. 
These  works  have,  therefore,  seldom  if  ever  been  undertaken, 
unless  at  the  requirement  of  others,  who,  dictating  both  the 
subject  and  its  details  according  to  their  own  peculiar  tastes 
and  wishes,  leave  nothing  wherein  the  superior  talents  of  the 
artist  can  be  displayed,  save  the  correctness  of  drawing  and  the 
elaborateness  of  execution.  A  man  of  genius  will  not  consent 
to  be  thus  trammelled,  or  follow,  for  the  attainment  of  a  precari¬ 
ous  recompense,  one  profession,  when,  by  bringing  to  the  exer¬ 
cise  of  another  the  same  amount  of  talent,  and  far  less  labor,  he 
may  at  once  give  scope  to  his  conceptions  and  advance  his 
worldly  interests. 

A  much  wider  field  than  presents  itself  for  the  exercise  of 
this  art  in  England,  is  certainly  offered  in  Catholic  countries, 
where  not  only  is  it  more  in  accordance  with  the  feelings  of 
the  people  to  ornament  their  religious  edifices,  but  where  a 
much  freer  scope  is  given  to  the  artist  in  the  choice  of  subjects 
for  embellishment.  Popular  legends  of  the  saints  in  honor  of 
whom  their  churches  are  named,  which  are  shut  out  by  our 
simpler  form  of  worship  and  severer  religious  discipline,  afford 
a  never-failing  source  whence  these  subjects  may  be  drawn ; 
while  he  whcT labors  for  the  adornment  of  a  Protestant  church, 
is  restricted  to  subjects  founded  upon  mere  scriptural  authority. 
England  has,  indeed,  within  the  last  half  century,  produced 
some  few  proficients  in  this  art,  whose  productions  would  do 
honor  to  any  country  :  but  the  encouragement  extended  towards 
these  talented  individuals  has  been  too  limited  to  raise  up,  as  in 
other  pursuits,  a  succession  of  masters ;  while  some,  by  whom 
it  has  at  first  been  embraced,  have  been  allured  from  it  by  the 
more  general  and  liberal  patronage  accorded  to  the  professors 
of  oil  painting. 

Staining  and  painting  on  glass  differ  in  some  respects  from 
all  other  styles  of  pictorial  embellishment.  They  agree,  how¬ 
ever,  generally  with  the  processes  used  in  painting  porcelain, 
not  only  in  the  nature  of  the  substances  to  be  embellished,  and 
in  the  materials  whence  the  colors  are  derived,  but  likewise  for 


226 


GLASS  MANUFACTURE. 


CHAP.  XIV. 


the  most  part  in  the  methods  used  for  the  application  of  those 
colors,  and  in  the  necessity  which  exists  for  fixing  them  by  ex¬ 
posure  to  a  high  degree  of  heat.  The  art  is,  indeed,  in  most 
particulars,  so  extremely  analagous  to  the  methods  employed 
for  painting  porcelain,  and  which  have  already  been  treated  of 
in  this  volume,  that  it  will  not  be  necessary  to  occupy  much 
space  in  its  description. 

The  colors  are  drawn  from  the  same  class  of  natural  sub¬ 
stances  as  afford  enamel  colors;  they  are  prepared,  and  for  the 
most  part  are  applied,  in  the  same  manner ;  while  any  difference 
which  may  be  found  to  exist  in  the  mode  of  fixing  and  bringing 
out  the  effect  of  colors  by  the  aid  of  fire,  are  more  referrible  to 
the  varied  forms  of  the  articles  than  to  any  actual  difference 
observable  between  the  habitudes  of  glass  and  porcelain. 

Boyle,  in  one  of  his  letters  on  the  subject  of  imbuing  glass 
with  metallic  colors,  wherein  are  detailed  some  experiments 
which  he  himself  made  in  order  to  obtain  a  ruby  color,  relates 
also  an  anecdote  of  an  artist,  who  wished,  for  some  purpose,  to 
prepare  an  amalgam  of  gold  and  mercury.  With  this  view  he 
kept  the  two  metals  for  some  time  together  in  a  state  of  fusion 
in  a  glass  retort,  when  this  at  length  burst  with  a  tremendous 
explosion.  Mr.  Boyle  adds,  that  he  saw  some  of  the  fragments, 
and  he  declares  them  to  be  of  the  finest  ruby  color  he  ever  be¬ 
held. 

Many  directions  are  to  be  found  in  the  works  of  old  writers 
for  the  composition  of  stains  and  colors.  Some  of  these  agree 
very  closely  with  recipes  in  use  at  present,  while  others  are 
evidently  incorrect  or  incomplete  ;  it  being  impossible,  by  fol¬ 
lowing  them,  to  obtain  the  colors  which  they  are  said  to  fur¬ 
nish.  There  appears  to  have  always  existed  a  spirit  of  exclu¬ 
sion  on  the  part  of  professors  of  this  art ;  and  it  has  been  said 
that  this  jealousy  has  even  weighed  with  those  among  them 
who  have  written  on  the  subject,  so  far  as  purposely  to  give 
false  directions,  that  students  might  be  deterred  from  the  fur¬ 
ther  prosecution  of  their  attempts.  It  is  more  charitable,  and 
at  the  same  time  more  consonant  with  probability,  to  imagine, 
that  the  errors  which  abound  in  these  works  are  owing  rather 
to  the  carelessness  of  transcribers  and  editors,  than  to  wilful 
misstatements  on  the  part  of  the  authors.  Let  this  be  as  it  may, 
it  still  is  certain  that  until  the  period  when  M.  Brongniart  pub¬ 
lished  the  results  of  his  experiments  and  practice  in  regard  to 
enamel  colors,  the  public  was  not  in  possession  of  any  informa¬ 
tion  whereon  reliance  could  safely  be  placed  for  their  produc¬ 
tion. 

Various  compositions  are  recommended  to  be  used  with  the 
colors  as  fluxes,  in  order  to  promote  their  fusion  when  exposed 


CHAP.  XIV.  STAINING  AND  PAINTING  GLASS.  22? 

to  the  heat  of  the  furnace :  these  compositions  are  termed  hard 
or  soft  fluxes,  in  proportion  as  they  require  a  greater  or  less 
amount  of  heat  for  their  perfect  fusion,  and  for  the  production 
of  their  full  effect  upon  the  metallic  oxides  with  which  they  are 
joined.  In  choosing  between  them,  regard  must  be  had  to  the 
peculiar  nature  of  the  individual  substance  or  compound  where¬ 
with  they  are  combined,  that  the  flowing  of  all  in  fusion  may 
take  place  as  nearly  as  possible  together.  With  this  view,  it  is 
evident  that  a  waste  both  of  time  and  labor  would  be  experi¬ 
enced,  if  any  hard  flux  were  used  with  an  oxide  which  could 
be  brought  to  melt  at  a  low  heat ;  and,  on  the  other  hand,  that 
it  would  be  still  more  improper  to  use  a  soft  flux  with  oxides 
which  are  more  refractory,  seeing  that  the  proper  incorporation 
of  the  two  substances  could  not  possibly  in  that  case  be  occa¬ 
sioned. 

Oxide  of  lead  forms  a  principal  ingredient  in  many  fluxes. 
It  is  necessary,  however,  to  be  sparing  in  its  use  where  it  is  re¬ 
quired  to  produce  pink  colors,  as  these  would  be  injuriously 
acted  upon  by  any  excessive  quantity  of  lead.  Its  place  may  in 
such  case  be  advantageously  supplied  by  borax. 

A  fluxing  compound,  very  generally  used,  is  made  by  the 
union  of  thirty-two  parts  of  flint  glass  with  twelve  parts  of 
pearl-ash,  and  two  parts  of  borax ;  which  composition  will  fuse 
at  a  medium  heat.  If  it  should  be  required  to  render  this  more 
fusible,  such  an  effect  may  be  gained  either  by  substituting  for 
the  pearl-ash  four  parts  of  red  oxide  of  lead,  or  by  increasing 
proportionally  the  dose  of  borax;  and  if,  on  the  other  hand,  it  is 
desired  to  produce  a  hard  flux,  this  end  may  be  attained  by 
omitting  the  borax  altogether,  and  adding  an  equal  quantity  of 
common  table  salt. 

The  directions  for  the  preparation  of  fluxes  for  porcelain, 
which  will  be  found  in  another  part  of  this  volume,  apply  equal¬ 
ly  to  those  which  are  to  be  used  with  glass,  and  it  would  be 
therefore  useless  to  repeat  them  here. 

When  enamel  colors  are  applied  to  glass,  they  are,  besides 
their  union  with  a  fluxing  material,  mixed  in  the  same  manner 
as  for  painting  on  porcelain,  with  some  substance  as  a  vehicle 
for  causing  them  to  flow  readily  from  the  brush,  and  at  the  same 
time  to  prevent  the  colors  from  blending  themselves  one  with 
the  other  during  the  operation.  Oil  of  lavender,  balsam  of 
capivi,  oil  of  turpentine  or  of  amber,  or  sometimes  gum-water, 
are  employed  as  this  vehicle.  The  choice  of  any  particular 
substance  must  depend,  as  in  the  painting  on  porcelain  bodies, 
upon  the  nature  of  the  coloring  matters  employed,  and  is  of  no 
real  consequence  to  the  ultimate  appearance  of  the  glass,  since 


GLASS  MANUFACTURE. 


CHAT.  XIV. 


228 


the  whole  will  be  entirely  evaporated  when  submitted  to  the 
intense  heat  of  the  furnace. 

The  coloring  compounds  having  been  previously  ground  with 
an  appropriate  flux  upon  either  a  porphyry  or  strong  plate- 
glass  palette,  by  means  of  a  muller  of  the  same  material,  must 
again  be  ground  in  the  same  manner,  and  reduced  to  a  proper 
consistency  with  the  vehicle  just  mentioned.  The  artist  will 
do  well  to  prepare  at  first  a  sufficient  quantity  of  every  color 
required  for  the  completion  of  the  object  which  he  has  in  hand  ; 
it  being  extremely  difficult,  if  not  impossible,  to  produce  tints 
identically  the  same  at  any  subsequent  time,  although  the 
greatest  attention  be  paid  to  the  proportions  of  their  ingredients. 
The  injury  which  may  be  thus  occasioned  to  the  beauty  of  the 
piece  need  not  be  insisted  upon. 

Many  objects  may  be  painted  on  glass  by  persons  who  have 
not  acquired  any  previous  knowledge  of  the  art  of  design.  The 
transparent  nature  of  the  material  enables  the  artist  to  see  dis¬ 
tinctly  both  the  outline  and  the  shading  of  any  pattern  which 
may  be  fixed  upon  its  under  side.  The  outlines  of  every  such 
pattern  should  be  decidedly  given ;  and  the  whole  contour  anc 
shading  must  be  at  once  obvious  when  looking  on  its  uppei 
surface.  When  the  pattern  paper  is  laid  horizontally  upon  th( 
glass,  it  must  be  secured  by  wafers  at  each  of  its  four  corners 
to  prevent  its  shifting  ;  the  glass  must  then  be  placed  upon  ar 
easel  similar  in  form  to  a  music-stand,  and  fixed  steadily  upoi 
the  table.  Means  should  also  be  taken  to  prevent  the  slipping 
of  the  glass  upon  the  easel,  by  passing  a  string  across  its  fact 
in  any  position  that  will  secure  this  object,  without  interfering 
with  the  subject  intended  to  be  drawn. 

To  support  the  arm  of  the  artist  while  he  is  employed  ii 
painting,  as  it  would  be  improper  for  him  to  touch  the  glass,  i 
will  be  necessary  to  use  a  rest  stick,  in  the  manner  observe' 
by  artists  who  paint  with  oil  colors. 

It  is  considered  advisable  to  trace  the  outline,  in  the  firs 
instance,  with  common  Indian  ink  much  diluted,  before  usinj 
for  the  purpose  the  pencil  color,  about  to  be  described:  th> 
reasons  for  which  are,  that  the  strokes  will  admit  of  easier  cor 
rection,  and  that  a  rough  line  will  be  thus  formed  upon  the  sin 
face  of  the  plate,  which,  drying  immediately  after  the  applies 
tion,  serves  to  direct  the  point  of  the  brush  when  charged  wit 
the  color,  and  to  occasion  the  delivery  of  the  latter  with  greate 
ease  and  regularity  than  would  be  otherwise  attainable  :  b 
this  means  the  artist  may  avoid  any  patching  or  altering  of  th 
outline,  which  would  seldom  fail  to  render  the  work  roug 
and  unsightly,  but  which  must  be  resorted  to  if  the  line 
prove  unequal  or  imperfect.  Faults  of  this  kind  may,  indeet 


CHAP.  XIV.  STAINING  AND  PAINTING  GLASS. 


229 


be  partially  corrected  at  any  period  of  the  process ;  but  as  the 
glass  must  be  fired  anew  after  each  application  of  color,  and 
as  the  firings  constitute  the  principal  part  of  the  expense,  it  is 
of  course  advisable  to  exercise  all  possible  carefulness,  in  order 
to  avoid,  as  far  as  possible,  the  necessity  for  their  repetition. 

The  color  most  usually  employed  for  drawing  the  outlines 
and  for  shading  different  subjects,  and  which  is  therefore  called 
by  artists  outline  or  pencil  color,  is  made  of  the  saflfon-colored 
oxide  of  iron  commonly  known  in  the  shops  by  the  name  of 
crocus  martis.  This  oxide  must  be  well  ground  in  combina¬ 
tion  with  an  equal  weight  of  soft  flux  upon  a  porphyry  or 
plate-glass  palette,  as  before  directed,  and  subsequently  also 
with  oil  of  amber  as  its  vehicle.  To  provide  for  the  preserva¬ 
tion  of  its  proper  degree  of  consistency,  the  addition  of  one  or 
two  drops  of  balsam  of  capivi  may  be  needed  ;  it  is  desirable, 
however,  to  make  as  sparing  use  as  possible  of  this  substance, 
which  sometimes,  when  evaporated  in  the  intense  heat  of  the 
kiln,  will,  through  its  greasiness,  indispose  the  glass  from 
taking  the  color  properly ;  and  little  vacancies  may  in  conse¬ 
quence  be  left  unoccupied,  and  requiring  to  be  subsequently 
supplied.  The  pencil  color  thus  prepared  is  a  dark-reddish 
brown,  and  remains  unaltered  by  the  heat  of  the  furnace.  In 
order  that  the  outline,  while  it  is  sufficiently  decided,  may  at 
the  same  time  be  fine  and  clear,  the  pencil  color  must  be  used 
as  little  moistened  as  will  admit  of  its  flowing  from  the  brush ; 
and  until  it  has  become  perfectly  dry  and  hard  upon  the  glass, 
no  subsequent  part  of  the  coloring  process  should  be  commenced. 

If  when  the  pattern  is  wafered  on  the  glass,  and  the  outline 
has  been  completely  traced,  it  is  desired  to  make  one  or  more 
copies  of  the  figure  upon  other  plates  of  glass,  this  may  be  done 
without  removing  the  paper  from  the  first,  by  simply  placing 
the  second  and  other  plates  in  succession  upon  that  to  which 
the  pattern  is  attached,  the  transparency  of  which  will  admit 
of  the  outlines  being  traced  with  the  same  facility  as  if  the 
pattern  had  been  transferred  to  each  individual  plate. 

The  best  crown-glass  is  generally  chosen  for  painting  or 
staining  as  being  most  transparent  and  free  from  color. 

The~colors  must  be  laid  on  with  a  long-haired  sable  pencil ; 
its  handle  must  be  of  a  length  which  will  allow  the  artist  to  use 
his  hand  with  freedom,  and  should  be  securely  attached  to  the 
brush,  so  that  the  two  cannot  become  disunited.  If  such  an 
accident  were  to  occur  as  the  falling  of  this  brush  charged 
with  color,  it  would  be  impossible  adequately  to  repair  the  mis¬ 
chief  by  any  means  short  of  obliterating  the  whole,  and  begin¬ 
ning  the  work  anew. 

The  shading  and  coloring  are  very  frequently  performed 


232 


GLASS  MANUFACTURE. 


CHAT.  XIV. 


will  considerably  heighten  and  bring  out  the  colors.  Should 
there,  however,  be  any  imperfections  either  in  the  stain,  or 
painting,  or  pencil  shading,  these  must  be  repaired  by  the  artist 
previous  to  consigning  the  glass  again  to  the  kiln. 

It  is  sometimes  wished  to  give  to  glass  the  appearance  of 
having  been  ground,  leaving  at  the  same  time  transparent  lines 
or  patterns  upon  its  surface,  the  effect  of  which  is  very  pleasing 
to  the  eye.  In  preparing  for  the  production  of  this  appearance, 
the  artist  uses  a  large  camel-hair  pencil,  the  end  of  which  is 
dipped  into  oil  of  amber,  so  as  to  take  up  only  a  small  quantity 
at  any  one  time  ;  and  with  this,  holding  the  brush  perpendicu¬ 
lar  to  the  glass,  every  part  of  the  latter  must  be  dabbed  so  that 
the  surface  will  be  dimmed  by  the  oil.  This  must  not  lie 
thicker  on  one  part  than  on  another,  and  should  by  no  means 
be  applied  in  sufficient  quantity  to  give  it  a  fluid  appearance. 
Taking  then  a  mixture,  composed  of  one  part  of  white  oxide 
of  tin,  with  three  parts  of  flux,  previously  well  ground  together, 
this  must  be  sifted  from  a  lawn  sieve  very  gently  over  the 
glass,  until  the  whole  surface  is  evenly  covered.  The  requi¬ 
site  quantity  of  this  powder  will  adhere  slightly  to  the  glass 
through  the  means  of  the  oil ;  and  when,  in  the  course  of  six 
or  eight  hours,  this  has  become  sufficiently  dry,  the  superfluous 
powder  must  be  lightly  removed  with  a  soft  brush  made  of 
badgers’  hair.  The  appearance  of  the  glass  will  now  perfectly 
resemble  that  which  has  been  ground. 

In  order  to  produce  lines  or  patterns  upon  its  surface,  that 
shall  have  the  usual  polish  and  transparent  quality  of  glass,  a 
pattern  must  be  drawn  upon  paper,  having  its  lines  sufficiently 
strong  to  be  visible  through  the  powder ;  and  this  being  fixed 
upon  the  reverse  side,  the  artist  with  a  blunt  wooden  instru¬ 
ment  scrapes  off  the  composition  in  lines  accordant  with  those 
of  the  pattern.  The  plate  of  glass  having  then  been  subjected 
to  burning  in  the  kiln,  it  will  be  found  that  the  powder  has 
been  partially  melted  by  the  heat,  and  is  so  firmly  united  to  the 
glass,  that  its  removal  will  be  extremely  difficult. 

It  now  remains  to  describe  the  particular  apparatus  and  pro¬ 
cess  used  for  burning-in  the  colors  which  have  been  applied  to 
the  surface  of  the  glass.  The  size  of  the  kiln  is  of  course  de¬ 
pendent  on  the  magnitude  and  number  of  the  pieces  of  glass 
upon  which  it  may  be  desired  to  operate  at  any  one  time.  It 
would  be  unwise  to  construct  one  of  larger  dimensions  than 
are  likely  to  be  needed  in  use,  as  the  due  heating  of  the  glass 
is  more  difficult  and  expensive,  in  proportion  as  the  relative 
size  of  the  furnace  is  increased. 

The  glass  is  placed  during  the  firing  in  a  close  iron  box  or 
oven,  which  is  called  a  muffle,  and  which  is  provided  with  hori- 


CHAP.  XIV.  STAINING  AND  PAINTING  GLASS.  233 

zontal  iron  shelves  placed  at  regular  distances  apart,  whereon 
the  plates  are  deposited.  The  relative  sizes  of  the  muffle  and 
furnace  are  such,  that  a  space  not  less  than  four  inches  remains 
between  the  two  on  every  side,  by  which  means  the  fire  may 
be  made  wholly  to  envelop  the  muffle.  This  receptacle  is  pro¬ 
vided  with  a  tube  proceeding  from  its  front,  and  narrowing  to¬ 
wards  its  extremity,  without-side  the  furnace  wall,  the  use  of 
which  tube  is  to  examine  the  state  of  the  glass  from  time  to 
time  during  the  process  of  firing.  The  iron  plates  for  support¬ 
ing  and  separating  the  glass,  and  which  are  fitted  to  the  shape 
of  the  muffle,  are  kept  at  their  proper  distances,  usually  about 
one  inch  asunder,  by  legs  of  the  requisite  length  placed  at  their 
four  corners.  The  shape  of  the  muffle  is  usually  wider  at  the 
top  than  at  the  bottom,  so  that  pieces  of  various  dimensions 
may  be  contained  in  its  different  compartments.  The  number 
of  these  bears  reference  to  the  size  of  the  apparatus,  some 
small  muffles  having  no  more  than  five  or  six,  while  others  of 
greater  dimensions  are  provided  with  double  that  number  of 
shelves. 

If  the  plates  of  glass  were  placed  in  immediate  contact  with 
the  iron  shelves  within  the  muffle,  the  metal  would  have  an 
injurious  effect  upon  some  colors.  The  iron  is,  besides,  liable 
to  be  warped  ;  and,  when  the  glass  was  brought  into  a  softened 
state  by  heat,  would  communicate  its  own  distorted  shape. 
Another  and  a  greater  evil  than  even  these  would  arise  from 
the  too  sudden  variations  of  temperature  whereunto  the  glass 
would  be  subjected,  owing  to  the  strong  conducting  power  of 
the  iron,  and  which  would  imminently  endanger  the  cracking 
of  the  glass. 

A  perfect  remedy  for  all  these  evils  is  found  in  previously 
preparing  a  smooth  and  even  bed  for  the  glass,  by  sifting 
pounded  whiting  to  the  depth  of  a  quarter  or  three  eighths  of 
an  inch  over  the  entire  surface  of  the  iron  shelves.  Upon  this 
bed  the  glass  must  be  deposited  with  every  possible  care,  so  as 
to  avoid  rubbing  the  colors. 

If  more  than  one  piece  is  committed  to  each  shelf,  they  must 
on  no  account  be  brought  into  contact,  nor  must  they  be  al¬ 
lowed  to  touch  or  even  to  approach  within  half  an  inch  of  the 
side  of  the  muffle.  When,  after  proceeding  in  this  manner, 
the  muffle  has  been  filled,  or  all  the  glass  that  is  ready  for 
burning  has  been  deposited,  the  cover  must  be  put  on  to  the 
muffle,  and  the  fire  lighted.  It  is  usual  to  employ  coke  and 
charcoal  as  fuel  for  burning  glass,  both  because  they  afford  a 
steadier  and  more  effective  heat  than  coal,  and  because  the  sul¬ 
phur  which  the  latter  so  commonly  contains  might  have  an  evil 
effect  upon  the  colors. 

U  2 


236 


GLASS  MANUFACTURE. 


CHAP.  XV. 


they  are  of  necessity  numerous,  yet  partake  of  the  simplicity 
observable  throughout  the  various  processes  of  the  manufacture. 

In  some  principal  establishments,  steam  power  is  used  for 
giving  motion  to  a  shaft  which  causes  the  revolution  of  numer¬ 
ous  large  wheels  or  drums  fixed  thereon,  and  each  of  these  being 
connected  by  a  band  with  a  pulley  on  the  axle  of  a  smaller 
wheel,  occasions  the  latter  to  revolve  with  great  celerity :  these 
small  wheels  are  the  cutting  instruments.  The  occupation  is 
frequently  carried  on  in  the  apartment  of  an  individual  work¬ 
man,  and  in  this  case,  only  one  large  wheel,  similarly  connected 
with  the  axle  of  one  of  smaller  diameter,  is  turned  by  means  of 
a  winch,  a  boy  being  employed  for  the  purpose.  In  all  other 
respects  the  process  is  identical,  whether  prosecuted  in  the  attic 
of  the  artisan,  or  in  the  spacious  factory  of  the  manufacturer. 

The  small  wheels  are  so  arranged,  that  each  can  be  unfixed 
without  difficulty,  and  another  substituted  of  a  form  better  suited 
to  the  work  in  hand,  or  of  a  material  more  adapted  to  the  stage 
of  the  process. 

As  regards  their  forms,  these  cutting  wheels  are  either  nar¬ 
row  or  broad — flat-edged — mitre-edged,  that  is,  with  two  faces 
forming  a  sharp  angle  at  their  point  of  meeting — convex  or  con¬ 
cave.  In  fact,  so  various  are  the  wants  of  the  workman,  that 
as  many  as  forty  or  fifty  wheels  having  differently  shaped  edges, 
are  to  be  found  in  the  workshop. 

The  materials  employed  in  the  formation  of  these  cutting  im¬ 
plements  are,  iron,  both  cast  and  wrought;  Yorkshire  stone; 
and  willow  wood.  Wrought  iron  is,  indeed,  only  used  for  cut¬ 
ters  of  the  narrowest  dimensions,  and  which  it  would  therefore 
not  be  possible  to  make  sufficiently  tough  of  cast  metal.  Iron 
wheels  are  used  only  for  the  first  or  roughest  part  of  the  opera¬ 
tion,  and  their  employment  is  even  dispensed  with  altogether, 
where  it  is  intended  that  the  pattern  shall  be  at  all  minute;  as 
the  metal  and  the  sand,  which  must  be  used  in  conjunction  with 
it,  would  act  too  roughly,  and  frequently  chip  away  portions  of 
the  glass.  For  such  minute  works,  and  for  smoothing  down  the 
asperities  which  will  always  be  occasioned  where  iron  cutters 
have  been  applied,  a  wheel  of  Yorkshire  stone,  moistened  with 
water,  must  be  used.  The  further  smoothing  and  subsequent 
polishing  of  the  cut  surfaces  are  effected  with  wooden  wheels : 
for  the  first  of  these  objects,  the  edge  is  dressed  with  either 
pumice-stone  or  rotten-stone  ;  and  for  imparting  the  high  de¬ 
gree  of  polish  that  is  requisite  for  properly  finishing  the  process, 
putty-powder  is  employed. 

Beneath  each  one  of  the  cutting  wheels,  a  small  cistern  is 
fixed  to  receive  the  sand,  water,  or  powder  which  has  been 
used ;  and  over  the  wheel,  a  small  keg  or  a  conical  vessel  is 


CHAP.  XV. 


GLASS  CUTTING. 


237 


placed,  the  cock  or  opening  at  the  bottom  of  which  is  so  situated 
and  regulated,  as  that  the  requisite  quantity  of  moisture  will  be 
imparted  from  it  to  the  wheel.  The  vessel  which  is  placed 
over  the  iron  wheel  is  furnished  with  fine  sand,  and  into  this 
water  is  admitted  in  such  quantity  as  will  insure  the  constant 
delivery  of  the  moistened  sand  upon  the  face  of  the  wheel  in 
such  proportion  as  the  workman  finds  most  desirable.  The 
emery  powder,  rotten-stone,  or  putty-powder,  are  applied  from 
time  to  time  as  required  by  the  workman,  on  the  edge  of  the 
smoothing  or  polishing  wheel. 

From  this  short  description  of  the  implements,  the  manner  of 
their  employment  will  be  readily  comprehended.  The  glass- 
cutter  seats  himself  on  a  stool  in  front  of  the  wheel ;  and  taking 
in  his  hand  the  glass  to  be  ornamented,  applies  this  to  the  face 
of  the  cutter,  the  correctness  of  his  eye  and  the  steadiness  of  his 
hand  being  called  into  requisition,  in  the  successive  applications 
to  the  wheel,  of  those  parts  of  the  glass  that  are  to  be  cut. 
Placed  at  his  right  hand  each  workman  has  a  small  tub  con¬ 
taining  water,  wherewith  from  time  to  time  he  washes  away 
the  particles  of  sand  or  powder  which  may  adhere  to  the  glass, 
that  he  may  the  better  judge  as  to  the  progress  of  his  work. 

It  may  readily  be  supposed  that,  in  conducting  a  process  of 
this  nature,  with  so  exceedingly  brittle  a  substance,  accidents 
will  often  occur  through  the  breaking  of  the  material.  The 
frequency  of  these  casualties  will  of  course  depend,  in  a  great 
measure,  upon  the  original  quality  of  the  material ;  and  this 
forms  one  reason  why  the  best  description  of  glass  is  generally 
chosen  for  the  purpose  of  being  cut. 

In  fitting  up  the  machinery,  it  is  plain  that  the  utmost  accu¬ 
racy  must  be  exercised.  If  the  cutting-wheels  were  allowed 
to  turn  upon  their  centres  with  the  smallest  degree  of  eccen¬ 
tricity,  it  would  be  quite  impossible  for  the  operator  to  proceed 
with  any  regularity  in  his  work,  or  to  produce  a  satisfactory 
effect. 

The  wages  of  glass-cutters,  in  common  with  those  of  men 
employed  in  the  different  manufacturing  processes  of  a  glass¬ 
house,  are  paid  according  to  the  work  which  they  deliver  in  a 
finished  and  perfect  state ;  so  that  if  any  accident  should  occur 
to  the  glass  while  in  their  hands,  as  is  frequently  the  case,  the 
workmen  cannot  claim  any  payment  for  the  labor  which  they 
may  already  have  bestowed  upon  it.  Every  man  who  follows 
the  occupation  of  a  glass-cutter  is  capable  of  executing  each 
part  of  the  process,  although  some  will  succeed  better  in  one 
branch  than  in  others.  In  large  establishments  there  is  gene¬ 
rally  such  a  choice  of  work,  that  every  workman  has  the  op¬ 
portunity  of  providing  himself  with  employment  in  that  branch 


238  GLASS  MANUFACTURE.  CHAP.  XV. 

which  he  prefers ;  besides  this,  two  or  more  men,  forming  a 
sort  of  partnership,  will  frequently  undertake  work  in  con¬ 
junction,  each  of  them  performing  that  branch  of  the  process 
which  he  feels  himself  qualified  to  execute  with  the  greatest 
success,  by  which  division  of  labor  the  whole  work  is  more  ex¬ 
peditiously  and  probably  also  more  satisfactorily  performed. 

The  grinding  of  glass,  or  frosting  it,  in  order  to  lessen  its 
transparency,  forms  a  branch  of  the  glass-cutter’s  art.  The 
objects  to  which,  in  the  present  day,  this  grinding  process  is 
most  commonly  applied,  are  shades  for  softening  the  light  dif¬ 
fused  by  table  lamps.  As  the  roughness  is  given  to  the  inner 
surface  of  these  glasses,  it  is  plain  that  they  cannot  be  applied 
to  the  cutting-wheel  for  the  purpose.  Instead  of  this,  the 
shades  are,  therefore,  fixed  in  a  lathe,  and  the  workman,  hold¬ 
ing  in  his  hand  a  piece  of  wood  which  he  covers  with  wet 
sand,  causes  this  to  rub  with  the  necessary  degree  of  force 
against  the  inner  surface  during  the  rapid  revolutions  of  the 
glass. 

The  amount  and  description  of  labor  bestowed  upon  articles 
which  pass  through  the  glass-cutter’s  hands,  must  necessarily 
enhance  their  money  value,  and  therefore  circumscribe  their 
use.  Nor  is  there  much  reason  to  look  for  the  discovery  of 
any  improvements  in  the  processes  whereby  that  labor  can  be 
so  abridged  as  that  the  manufacture  will  be  brought  within  the 
reach  of  a  larger  number  of  consumers.  Under  this  view,  any 
method  of  ornamenting  glass  which  can  be  offered  as  a  toler¬ 
able  substitute  for  cutting  it,  is  likely  to  be  favorably  received 
by  the  public. 

Such  an  invention  has  recently  been  made  the  subject  of  a 
patent,  under  which  glass  vessels,  having  a  variety  of  shapes, 
are  formed  with  ornamental  figured  patterns  impressed  upon 
them. 

The  method  of  producing  these  patterns  is  sufficiently  sim¬ 
ple,  and  consists  in  placing  a  quantity  of  melted  glass  within  a 
metallic  mould  of  the  required  form,  in  the  lower  division  of 
which  the  desired  pattern  is  engraved ;  and  in  then  bringing 
down  the  upper  section  of  the  mould,  and  pressing  the  melted 
glass  between  the  two.  The  only  skill  required  for  the  opera¬ 
tion  is  that  of  apportioning  rightly  the  quantity  of  melted  glass 
which  is  required  for  exactly  filling  the  mould,  so  as  to  take  a 
faithful  impression  of  the  engraved  pattern.  The  two  parts  of 
the  mould  are  connected  together  by  means  of  a  hinge,  and 
the  upper  portion  is  provided  with  a  long  handle,  which  acts  as 
a  lever  for  imparting  the  requisite  pressure.  The  lower  sec¬ 
tion  is  composed  of  two  pieces,  which  being  opened,  the  glass 


CHAP.  XV.  ETCHING  ON  GLASS.  239 

may  be  removed  from  the  mould  almost  at  the  moment  of  its 
formation. 

Intended  as  a  substitute  for  cutting,  this  art  must  certainly 
be  considered  inferior.  The  patterns  imparted  by  the  mould 
are  deficient  in  the  degree  of  sharpness  which  is  imparted  by 
the  wheel.  On  the  other  hand,  a  description  of  ornament  may 
be  thus  adopted,  which  is  otherwise  unattainable ;  the  figures 
may  be  either  raised  or  depressed,  and  patterns  the  most  minute 
and  intricate  may  be  produced.  Armorial  bearings,  in  particu¬ 
lar,  may  thus  be  represented,  in  a  manner  far  superior  to  any 
engraving,  not  only  as  the  glass  will  everywhere  retain  its 
polish,  but  also  because  figures  may  be  given  in  relief.  Be¬ 
tween  the  cost  of  the  two  processes  there  cannot  be  any  com¬ 
parison. 

Many  specimens  are  preserved  in  collections  of  ancient  glass 
which  are  ornamented  with  raised  figures.  These  have  been 
■  most  probably  produced  by  pressure  within  a  mould  while  yet 
softened  by  heat,  such  a  practice  being  one  of  great  antiquity. 
Engraved  figures  were  likewise  executed  upon  hollow  vessels 
by  the  old  Greek  artists;  and  that  celebrated  engraver  on 
stones,  Lawrence  Natter,  affirms,  in  his  “  Treatise  on  the  An¬ 
tique,  when  compared  with  the  Modern  Method  of  Engraving 
on  Precious  Stones,”  that  the  same  kind  of  instruments  were 
used  for  the  production  of  these  relics  of  antiquity,  as  were 
employed  for  the  same  purpose  at  the  time  when  he  wrote.  He 
considers  that  the  old  artists  undoubtedly  used  a  wheel,  which 
moved  in  a  horizontal  direction  above  the  table  at  which  they 
wrought ;  and  this  opinion  is  in  agreement  with  a  passage  in 
Pliny  (Hist.  Nat.  lib.  xxxvi.  cap.  26.) : — “  Aliud  flatu  figura- 
tur,  aliud  torno  teritur,  aliud  argenti  modo  Cfelatur.”  On  the 
other  hand,  to  agree  with  Natter  would  be  to  deprive  Lehmann 
of  his  reputation  as  an  inventor,  although  he  may  still  be  en¬ 
titled  to  the  honor  of  having  revived  an  art  which  had  become 
obsolete;  and  this,  in  the  opinion  of  the  learned  antiquarian 
Caylus,  himself  the  re-inventor  of  a  sister  art,  is  the  amount 
of  merit  whereto  Lehmann  may  justly  lay  claim. 

In  the  middle  of  the  sixteenth  century,  when  glasses  manu¬ 
factured  in  the  Venetian  states  enjoyed  the  highest  reputation 
throughout  Europe,  it  was  common  to  find  these  ornamented 
by  engravings  executed  with  the  diamond.  More  than  an  hun¬ 
dred  years  had  elapsed  from  that  period,  when  Henry  Schwan- 
hard,  a  pupil  of  Lehmann,  was  incited  by  the  accidental  cir¬ 
cumstance  of  the  corrosion  of  his  spectacle  glass,  to  a  method 
of  etching  on  glass  by  means  of  some  powerful  acid  liquor. 
His  manner  of  preparing  this  liquor  was  kept  secret  by  him ; 
and  as  no  fluid,  save  fluoric  acid,  with  which  we  are  acquaint- 


GLASS  MANUFACTURE. 


CIIAf.  XV. 


240 


ed,  has  the  property  of  acting  upon  the  surface  of  glass,  while 
the  discovery  of  this  powerful  menstruum  was  not  brought  be¬ 
fore  the  world  prior  to  the  publication  of  Scheele’s  experiments 
in  1771,  it  is  much  to  be  regretted  that  the  secret  of  Schwan- 
hard  was  suffered  to  go  with  him  to  the  grave. 

The  method  pursued  by  this  artist  in  the  application  of  his 
discovery  was  different  from  that  which  is  practised  at  present. 
This  is,  to  coat  over  the  entire  surface  of  the  glass  with  var¬ 
nish,  and,  through  this  coating,  to  trace  out  the  intended  fig¬ 
ures,  leaving  the  glass  exposed  to  the  action  of  the  acid  only 
in  those  parts  which  are  to  be  occupied  by  the  figures.  Schwan- 
hard,  on  the  contrary,  first  traced  the  figures,  and,  having  filled 
the  outline  on  the  glass  with  varnish,  applied  his  corrosive  fluid 
to  the  remainder  of  the  surface.  By  this  means  the  figures 
were  left  in  relief,  and  with  their  original  polish,  the  effect  of 
which  was  pleasing,  and  totally  dissimilar  to  the  appearance  of 
engravings  with  the  diamond,  which  latter  circumstance  it 
probably  was  that  incited  the  artist  to  the  adoption  of  his  pecu¬ 
liar  method,  since  his  productions  would,  by  that  means,  be 
more  readily  distinguished  from  the  works  of  others. 

The  varnish  employed  by  artists  for  defending,  where  it  is 
requisite,  the  surface  of  the  glass  from  the  corroding  power  of 
the  acid,  is  usually  either  a  solution  of  isinglass  in  water,  or 
common  turpentine  varnish  mixed  with  a  small  proportion  of 
white  lead. 

By  the  aid  of  a  very  few  implements,  the  art  of  etching  on 
glass  may  be  rendered  a  pleasing  occupation  for  amateurs. 
Good  crown-glass  is  the  most  proper  to  be  chosen  for  this  pur¬ 
pose.  Having  selected  a  square  pane  of  the  proper  size,  this 
should  be  first  heated  by  immersion  in  a  sand-bath,  and  then 
rubbed  over  with  purified  bees’-wax,  the  temperature  of  the 
glass  being  such  as  to  cause  the  wax  to  melt  completely  and 
uniformly  over  its  surface.  The  pane,  thus  covered,  must  then 
be  set  aside  to  cool ;  and  it  is  important  to  observe,  that  every 
part  of  its  face  must  be  protected  by  this  coating  of  wax; 
which,  however,  need  not  be  thick,  and  indeed  should  not  be 
applied  in  sufficient  quantity  to  render  the  glass  opaque. 

A  paper  having  the  design  boldly  drawn  upon  it,  may  then 
be  attached  to  the  unwaxed  under  side  of  the  glass ;  and  this 
drawing  will  greatly  assist  the  artist  in  performing  the  next 
process,  that  of  tracing  the  design  through  the  wax.  The  best 
kind  of  tool  for  executing  this  operation  is  a  carpenter’s  brad¬ 
awl,  which,  as  it  is  flattened  at  the  end  in  one  direction,  and 
rounded  in  another,  may,  according  to  the  position  wherein  it 
is  held,  be  easily  made  to  trace  lines  having  the  requisite  and 
different  degrees  of  fineness.  The  point  of  a  penknife,  or  any 


CHxVP.  XV. 


ETCHING  OF  GLASS. 


241 


similar  implement,  may  be  used  as  a  substitute  for  the  brad-awl, 
and  with  almost  equal  efficacy.  In  tracing  these  lines,  the  artist 
must  be  mindful  that  his  instrument  lays  bare  the  surface  of  the 
glass  throughout  the  whole  extent  of  the  strokes. 

A  shallow  evaporating  basin  of  Wedgwood  ware  must  next 
be  employed.  Its  size  should  be  such  as  will  include  within  its 
area  every  part  of  the  design;  and  it  must  at  the  same  time  be 
sufficiently  small  to  be  completely  covered  when  the  pane  of 
glass  is  made  to  rest  upon  its  edge.  Some  coarsely  powdered 
fluor  spar  must  then  be  placed  in  the  basin,  together  with  a 
quantity  of  strong  sulphuric  acid,  sufficient  to  form  with  it  a 
thin  paste,  when  the  two  substances  must  be  well  mixed  to¬ 
gether  by  stirring  them.  The  quantity  of  fluor  spar  must  of 
course  be  regulated  by  the  size  of  the  etching ;  and  it  may  be 
a  sufficient  guide  on  that  head,  to  recommend  that  two  ounces 
of  the  coarse  powder  be  used  when  the  basin  is  capable  of  con¬ 
taining  a  pint :  these  basins  are  readily  procurable  from  any  re¬ 
spectable  dealer  in  earthenware. 

As  soon  as  the  acid  and  fluor  spar  are  properly  incorporated 
together,  the  pane  of  glass  should  be  placed  upon  the  basin, 
with  the  waxed  side  downwards,  and  a  moderate  degree  of  heat 
must  be  applied  to  the  bottom  of  the  basin :  somewhere  between 
120  and  140  degrees  of  Fahrenheit’s  scale  will  be  found  most 
eligible.  Perhaps  the  best  means  of  providing  a  steady  heat 
for  this  purpose  is  offered  by  the  sand-bath,  which  was  used  for 
heating  the  glass  before  applying  the  wax.  On  this  subsequent 
occasion,  however,  the  temperature  must  never  be  sufficiently 
high  to  melt  the  wax,  which  in  that  case  would  run  over  the 
glass,  and  wholly  destroy  the  effect  of  the  etching. 

Very  soon  after  this  application  of  heat,  fumes  of  fluoric  acid 
will  rise  copiously  from  the  basin,  and  attack  the  unprotected 
portions  of  the  glass.  When  the  basin  and  its  contents  are  once 
thoroughly  warmed,  the  heat  of  the  sand-bath  may  be  advan¬ 
tageously  diminished. 

After  the  glass  has  been  thus  exposed  during  half  an  hour, 
it  may  be  removed  from  the  basin ;  and  first  being  rinsed  in 
water,  for  the  purpose  of  diluting  or  washing  away  the  fluoric 
acid,  the  wax  may  be  scraped  off  with  a  common  table-knife ; 
the  design  will  then  be  found  perfectly  etched  upon  the  surface 
of  the  glass. 

A  metallic  basin  will  answer  perfectly  for  generating  the  flu¬ 
oric  acid ;  but  it  will  be  altogether  improper  to  use  any  glazed 
vessels  for  the  purpose,  as  the  vitreous  coating  of  such  would  be 
entirely  destroyed. 

In  performing  this  process,  it  is  necessary  to  use  some  cau¬ 
tion  ;  as  fluoric  acid,  if  brought  into  contact  with  the  skin,  will 


GLASS  MANUFACTURE. 


CHAP.  XV. 


242 


quickly  disorganize  it,  and  produce  wounds  which  may  be  pain¬ 
ful  and  troublesome ;  a  very  little  carefulness  will,  however, 
suffice  for  preventing  any  accident  of  this  nature. 

When  it  is  required  thus  to  engrave  other  than  plane  sur¬ 
faces,  another  arrangement  must  be  provided :  the  glass  must 
be  exposed  to  the  fumes  of  fluoric  acid  in  some  deep  vessel ; 
without,  however,  being  suffered  to  come  in  contact  with  the 
pasty  compound  whence  the  acid  fumes  arise ;  and  the  whole 
should  be  covered  over,  to  confine  and  retain  those  fumes,  so 
that  they  may  fully  act  upon  the  glass. 

Articles  made  of  flint  glass  are  sometimes  very  tastefully  or¬ 
namented,  by  inclosing  within  their  substance  various  objects 
formed  out  of  bodies  which,  being  less  fusible  than  glass,  will 
not  be  altered  in  their  form  or  nature  by  the  heat  contained  in 
this  at  the  moment  of  their  introduction. 

The  art  was  first  attempted  about  fifty  years  ago,  by  a  glass 
manufacturer  in  Bohemia,  who  sought  to  incrust  small  figures 
made  with  a  grayish  kind  of  clay.  His  success  in  this  attempt 
was  but  moderate ;  the  material  of  which  he  made  choice  for 
his  figures,  expanded  and  contracted  very  unequally  with  the 
surrounding  glass,  and  their  adhesion  to  it  was  consequently 
imperfect. 

The  successful  accomplishment  of  this  pleasing  art  has  long 
been  a  favorite  object  with  the  French  manufacturers,  who 
have  been  unsparing  of  expense  in  their  efforts  for  its  perfec¬ 
tion.  For  a  long  time,  however,  their  success  was  small,  and 
the  specimens  produced  by  them  were  so  costly,  that  but  little 
encouragement  was  offered  on  the  part  of  purchasers.  The 
subject  at  that  time  principally  chosen  for  the  exercise  of  this 
art,  was  a  medallion  of  Napoleon,  whose  courtiers  evinced  the 
desire  of  possessing  his  likeness  in  this  imperishable  form,  as 
being  emblematic  of  their  own  unalterable  attachment !  Im¬ 
provements  have  since  been  made  by  the  French  artists,  which 
have  enabled  them  to  reduce  the  cost  of  these  incrustations 
within  more  moderate  bounds;  but  their  manufacturers  have 
hitherto  mostly  restricted  themselves  to  the  ornamenting  in  this 
manner  of  scent-bottles  and  trinkets. 

A  few  years  ago  one  of  the  most  considerable  London  glass 
manufacturers  discovered  the  means  of  attaining  to  a  higher  de¬ 
gree  of  success,  and  is  now  enabled  thus  to  ornament,  in  a  very 
tasteful  manner,  various  objects  of  considerable  size ;  employing 
for  the  purpose  substances  whose  property  it  is  to  expand  and 
contract  equally  with  glass  upon  exposure  to  altered  tempera¬ 
tures.  This  interesting  art  can  by  this  means  be  applied  to 
represent  ornaments  of  almost  every  description.  The  appear¬ 
ance  most  usually  given  to  them  is  that  of  silver ;  but  as  the 


CHAP*  XVI. 


243 


Reaumur’s  porcelain. 

metallic  oxides  may  be  employed  for  coloring  the  substances 
previous  to  their  incrustation,  every  variety  of  hue  that  can  be 
used  in  enamel  painting  may  also  be  imparted. 


CHAP.  XVL 

ON  THE  DEVITRIFICATION  OF  GLASS. 

First  observed  by  Neumann. — Experiments  of  Reaumur. — Substance  known 
as  Reaumur’s  Porcelain. — Inappropriateness  of  this  name. — Uses  to  which 
the  Substance  may  be  applied. — Common  Bottle  Glass  most  proper  for  this 
Conversion. — Method  of  effecting  the  Change. — Produced  solely  by  Heat. 
—Experiments  of  Dr.  Lewis.— Revitrification.— Experiments  of  Sir  James 
Hall.— Proposal  suggested  thereby. — Observations  of  Guyton-Morveau. — 
Artificial  Intaglios. — Mock  Onyxes. — Power  of  Devitrified  Glass  to  bear 
sudden  Changes  of  Temperature.— Experiments  with  Colored  Glass. — 
Glass  devitrified  by  burning  Lava. — The  Process  promoted  by  multiply¬ 
ing  the  Ingredients  of  Glass.— Devitrified  Glass  conducts  Heat  more  per¬ 
fectly  that  when  vitreous.— Becomes  a  Conductor  of  Electricity.— Retains 
this  Property  when  revitrified. 

It  was  observed  very  long  since  by  Neumann,  that  some 
kinds  of  glass,  if  exposed  during  any  considerable  time  to  a 
high  degree  of  heat,  but  below  their  point  of  fusion,  are  so  far 
changed  in  their  properties  and  texture  as  to  become  opaque, 
fibrous,  and  tough ;  and  so  hard  as  to  give  abundant  sparks  if 
struck  with  steel,  to  cut  any  common  glass  readily,  and  to  be 
scarcely  susceptible  of  abrasion  by  filing.  It  has  also  been 
found,  that  in  taking  this  form,  glass  so  far  alters  its  nature  as 
regards  its  qualities  of  expansion  and  conducting  of  heat,  that 
it  will  bear  a  sudden  transference  from  freezing  to  boiling 
water. 

That  indefatigable  naturalist,  M.  Reaumur,  made  various 
experiments  and  observations  on  this  phenomenon  ;  and,  in  the 
year  1739,  communicated  the  result  of  these  to  the  Royal  Acad¬ 
emy  of  Sciences  in  Paris.  The  subject  becoming  by  this  means 
more  generally  known,  glass,  when  thus  converted,  obtained, 
and  has  since  kept  the  name,  of  Reaumur's  porcelain  ;  a  desig¬ 
nation  which  it  owes  to  its  appearance  rather  than  to  its  real 
properties,  which  do  not  at  all  entitle  it  to  be  classed  with  por¬ 
celain.  It  is  probably  owing  to  the  inappropriate  name  which 
the  substance  thus  acquired,  that  so  little  has  been  done  to¬ 
wards  a  true  development  of  the  facts  and  circumstances  at¬ 
tendant  upon  the  devitrification  of  glass.  Even  the  greater 
number  of  such  scientific  men  as  for  a  time  entered  upon  the 
investigation,  limited  their  labors  to  experiments  with  various 
cementing  substances,  that  they  might  arrive  at  the  discovery 


244 


GLASS  MANUFACTURE. 


CHAP.  XVI. 


of  that  one  which  would  insure  the  concurrence  of  the  greatest 
number  of  good  qualities  that  should  be  found  in  porcelain. 
The  futility  of  these  experiments  has  since  been  made  evident; 
and  it  must  be  regretted  that  the  same  amount  of  research  as 
was  thus  unprofitably  bestowed,  has  not  been  given  to  elucidate 
the  actual  properties  of  devitrified  glass,  and  to  render  it  prac¬ 
tically  serviceable  to  society. 

Reaumur  was  of  opinion  that  its  quality  of  resisting  alterna¬ 
tions  of  temperature,  its  toughness,  as  well  as  the  power  it  pos¬ 
sesses  of  withstanding  the  action  of  acid  liquids,  render  this  por- 
celainous  glass  well  qualified  for  the  formation  of  chemical  ves¬ 
sels.  The  same  opinion  has  been  equally  held  and  declared  by 
other  philosophers  who  have  brought  their  minds  to  the  inves¬ 
tigation  of  the  subject ;  and  it  appears  singular  that  their  sug¬ 
gestion  should  not,  consequently,  have  been  very  generally  re¬ 
duced  to  practice.  This  circumstance  must  further  excite  sur¬ 
prise,  when  it  is  considered  in  how  many  important  operations 
of  the  laboratory  such  a  substitute  for  metallic  vessels  would  be 
advantageous.  In  operating  upon  any  practical  scale,  the 
chemist  is  driven,  for  want  of  such  a  substitute,  either  to  the 
employment  of  metals  which  are  liable  to  be  injuriously  acted 
upon  by  the  matters  under  process,  or  is  compelled  to  adopt 
vessels  of  platinum,  the  expensiveness  of  which  places  them 
beyond  the  prudent  reach  of  most  persons.  In  one  instance,  a 
manufacturer  of  pharmaceutical  preparations,  who  is  exceed¬ 
ingly  particular  as  to  the  absolute  purity  of  his  productions,  has 
recently  incurred  the  expense  of  constructing  a  pan  of  unalloy¬ 
ed  silver,  forty  inches  in  diameter,  wherein  to  evaporate  vege¬ 
table  extracts,  many  of  which,  in  some  degree  or  other,  act 
upon  and  are  impregnated  by  copper. 

Could  vessels  formed  of  this  fibrous  glass  be  adopted  with 
safety,  there  would  be  nothing  in  their  cost,  especially  when  of 
moderate  size,  to  prevent  their  general  adoption.  The  only 
circumstance  hitherto  assigned  against  this  adoption  is,  that  al¬ 
though  the  inner  texture  of  the  glass  is  fine  and  white,  the  sur¬ 
face  is  coarse  and  of  a  dirty  appearance ;  but  this  must  be 
thought  a  very  insufficient  cause  for  foregoing  such  decided 
advantages  as  are  apparently  offered  through  its  employment. 

All  kinds  of  glass  are  not  equally  qualified  to  undergo  this 
conversion ;  with  some  descriptions,  indeed,  it  will  not  ensue. 
Not  any  vitreous  compound  seems  altogether  proper  for  it,  with 
the  exception  of  common  green  bottle-glass,  and  perhaps  also 
the  ordinary  kinds  of  window  glass. 

The  method  commonly  employed  for  effecting  the  change  is 
as  follows  : — The  glass  vessel  is  placed  within  a  larger  earthen 
vessel,  in  the  same  manner  as  is  pursued  for  baking  porcelain. 


chap.  xvi.  Reaumur’s  porcelain.  245 

The  entire  space  unoccupied  by  the  glass  is  next  filled  by  pour¬ 
ing  into  the  vessel  fine  white  sand,  or  powdered  gypsum,  so 
that  the  glass  shall  not  be  allowed  at  any  point  to  come  into 
contact  with  the  earthen  case.  The  containing  vessel  is  then 
covered  down,  securely  luted,  and  the  whole  is  placed  within 
the  furnace. 

It  was  for  some  time  generally  imagined,  that  in  this  process, 
which  is  very  similar  to  that  which  is  known  to  chemists  under 
the  name  of  cementation,  the  glass  owes  the  change  which  it 
undergoes  to  some  chemical  action  of  the  gypsum  upon  its  sub- 
stance°:  but  this  has  been  proved  erroneous.  It  is  shown  by  Dr. 
Lewis,  in  the  detail  of  his  various  experiments,  that  not  only 
may  the  nature  of  the  powder  be  almost  infinitely  varied,  with¬ 
out  in  the  least  affecting  the  operation,  as  far  as  regards  the  al¬ 
tered  texture  of  the  glass,  but  that  the  change  equally  and  iden¬ 
tically  goes  forward  in  the  absence  of  all  cementing  substance ; 
a  fact  which  is  conclusive  upon  the  subject,  and  which  proves 
that  whatever  may  be  the  particular  substance  employed, 
whether  sand,  bone-ash,  chalk,  or  gypsum,  it  acts  merely  by  af¬ 
fording  mechanical  aid,  sustaining  the  glass  in  its  proper  form 
during  the  period  when  it  is  softened  by  heat,  and  when,  if  de¬ 
prive!  of  such  support,  it  would  be  liable  to  irreparable  injury 
in  falling  together  by  means  of  its  own  gravity. 

In  the  course  of  experiments,  which  are  detailed  by  him  at 
some  length*  Dr.  Lewis  placed  several  pieces  of  common  wine 
bottles  into  crucibles,  pouring  over  them  the  requisite  quanti¬ 
ties  of  white  sand,  and  placing  them  in  a  proper  furnace,  where¬ 
in  they  were  heated  during  many  hours.  In  order  to  ascertain 
the  progress  of  the  change,  pieces  were  withdrawn  from  time  to 
time  for  examination.  Those  pieces  which  were  first  taken  out, 
after  having  been  during  several  hours  in  the  furnace,  but  with¬ 
out  being  heated  to  redness,  exhibited  no  sort  of  change  what¬ 
ever.  in  a  low  red  heat  the  change  went  forward  very  slow¬ 
ly,  but  still  was  quite  perceptible ;  while  in  a  strong  red  heat 
approaching  to  whiteness,  and  which  only  just  avoided  that  de¬ 
gree  of  intenseness  which  would  have  melted  the  glass,  the 
change  went  on  rapidly,  beginning  at  each  surface,  and  spread¬ 
ing  towards  the  middle ;  so  that,  in  two  hours,  the  substance 
had  assumed  throughout  the  appearance  of  porcelain. 

The  glass  became  first  of  a  bluish  color  on  the  surface,  and 
exhibited  a  very  sensible  diminution  of  its  transparency.  After 
this,  it  gradually  became  white  and  more  opaque  ;  the  texture 
no  longer  continued  vitreous,  but  became  fibrous,  as  already  de¬ 
scribed  ;  and  these  fibres  were  disposed  nearly  parallel  to  each 


*  Commercium  Philosophico-technicum,  p.  150. 

V  2 


246 


GLASS  MANUFACTURE. 


CHAP.  XVI. 


other,  and  transverse  to  the  thickness  of  the  piece.  The  fibres 
from  both  surfaces  meeting  in  the  middle,  formed  there  a  kind 
of  partition,  in  which  cavities  were  occasionally  perceptible. 
By  degrees  this  opacity  and  fibrous  change  were  completed,  the 
blue  color  disappeared,  and  was  succeeded  by  a  dull  white  or 
dun  color. 

When  exposure  to  the  same  high  degree  of  heat  was  con¬ 
tinued  after  the  production  of  this  effect,  the  glass  was  seen  to 
undergo  a  still  further  change  of  texture  :  the  fibres  appeared 
to  be  divided  or  cut  into  grains ;  beginning,  as  before,  at  the 
outer  ends,  and  proceeding  onwards  towards  the  middle,  until 
the  entire  substance  assumed  a  granular  form,  similar  to  ordi¬ 
nary  porcelain.  A  still  further  continuance  of  heat  caused  the 
grains,  which  at  first  were  fine  and  glossy,  to  become  enlarged 
and  dull,  and  to  change  from  a  compact  to  a  porous,  and  at 
length  to  a  friable  substance,  resembling  a  slightly  cohering 
mass  of  white  sand,  not  easily  distinguishable  from  that  wherein 
it  was  embedded. 

If  glass,  which  has  been  withdrawn  from  the  furnace  at  the 
time  it  has  assumed  the  fibrous  state,  be  afterwards  subjected  to 
a  very  strong  heat,  it  will  melt  into  a  semi-transparent  mass, 
and  may  be  drawn  out  in  strings,  which  on  cooling  are  found  to 
have  lost  their  fibrous  quality,  and  to  have  resumed  their  for¬ 
mer  vitreous  state,  being  no  harder  than  before  the  original 
cementation.  This  fusion  of  porcelainous  glass  cannot,  how¬ 
ever,  be  effected,  without  the  application  of  a  degree  of  heat 
considerably  more  intense  than  is  required  for  melting  glass  in 
its  more  usual  form ;  and  it  is  also  found  that  the  farther  the 
process  of  cementation  has  been  carried,  the  higher  must  the 
temperature  be  raised  for  its  fusion ;  so  that  specimens  which 
have  been  rendered  granular  are  much  more  refractory  than 
such  as  are  simply  fibrous. 

Although,  throughout  the  experiments  of  Dr.  Lewis,  no  dif¬ 
ference  in  the  actual  properties  of  Reaumur’s  porcelain  follow¬ 
ed  the  employment  of  different  substances  for  embedding  the 
glass, — its  internal  color,  hardness,  texture,  and  the  regular 
succession  of  its  changes  being  the  same  in  all  cases ; — yet  con¬ 
siderable  difference  was  occasioned  in  its  outward  color.  If 
charcoal  or  soot  had  been  used,  these  produced  a  deep  black 
color,  which  was  not  affected  by  long  exposure  to  heat  in  an 
open  furnace.  Clay  or  sand  which  was  colored,  communicated 
different  shades  of  brown  ;  and  white  earths  gave  either  gray 
or  brown  tinges.  The  greatest  degree  of  whiteness  followed 
upon  the  use  of  white  sand,  calcined  flints,  or  gypsum  ;  and  the 
highest  state  of  glossiness  or  brightness  was  caused  by  the  em¬ 
ployment  of  pipe-clay. 


chap.  xvi.  reaumttr’s  porcelain.  247 

In  the  account  published  by  Sir  James  Ilall  of  his  highly  in¬ 
teresting  course  of  experiments  on  the  effects  of  compression 
in  modifying  the  action  of  heat  upon  a  certain  class  of  substan¬ 
ces,  incidental  mention  is  made  of  an  important  circumstance 
connected  with  this  change  in  the  texture  of  glass,  and  which 
seems  to  point  the  way  towards  the  institution  of  a  further 
course  of  useful  investigations. 

Having  placed  in  the  closed  end  of  a  porcelain  tube  a  portion 
of  the  substance  which  he  was  about  to  subject  to  the  action  of 
heat  under  pressure,  it  became  necessary  to  introduce  likewise 
within  the  tube  some  other  substance,  which  could  be  brought 
to  such  a  state  as  would  oppose  an  effectual  barrier  against  the 
communication  of  the  principal  substance  with  the  atmosphere. 
The  use  of  various  bodies  was  attempted  for  this  purpose,  and 
each  was  successively  rejected  as  inadequate.  Among  these, 
Sir  James  determined  upon  trying  the  effect  of  pounded  glass; 
which,  being  placed  within  the  tube,  above  and  nearly  in  con¬ 
tact  with  the  principal  substance,  could  be  subjected  to  such  a 
degree  of  heat  as  would  fuse  the  glass,  while  the  closed  end  of 
the  tube  might  be  sufficiently  withdrawn  from  the  action  of  the 
furnace ;  and  when,  in  the  prosecution  of  the  actual  experiment, 
this  end  should  come  to  be  placed  in  the  strongest  heat,  that 
portion  of  the  tube  in  which  the  then  compact  body  of  glass  was 
contained  could  be  equally  removed  from  a  temperature  which 
would  again  alter  its  form. 

The  description  of  glass  accidentally  chosen  by  Sir  James 
Hall  for  his  experiment,  was  that  which  is  best  of  all  qualified 
for  conversion  into  Reaumur’s  porcelain.  Having  introduced 
the  tube  wherein  the  pounded  glass  was  contained  within  a 
muffle  heated  to  the  temperature  of  20°  of  Wedgwood’s  scale, 
3677°  Fahrenheit,  he  discovered,  that  in  the  space  of  one 
minute  it  entered  into  a  state  of  viscid  agglutination,  similar  to 
that  of  honey;  and  that  when  only  one  more  minute  had  elaps¬ 
ed,  the  entire  particles  were  consolidated  into  a  firm  compact 
mass  of  Reaumur’s  porcelain :  during  the  short  period  here  men¬ 
tioned,  the  heat  of  the  muffle  had  been  uniformly  sustained  at 
the  same  degree. 

If  a  solid  cylinder  of  glass,  having  the  same  bulk  as  the  pow¬ 
der  thus  placed  within  the  tube,  had  been  exposed  to  the  same 
temperature,  it  would  equally  have  undergone  a  change  from 
the  vitreous  to  a  fibrous  state ;  but  the  time  required  would 
have  amounted  to  at  least  an  hour. 

The  result  of  the  discovery  thus  unexpectedly  made  by  Sir 
James  Hall,  renders  it  probable,  that  if  common  green  bottle- 
glass,  previously  ground  to  powder,  were  introduced  within  ap¬ 
propriate  moulds,  and  exposed  to  an  adequate  temperature,  it 


248  GLASS  MANUFACTURE.  CHAP.  XVI. 

would  speedily  and  satisfactorily  be  converted  into  vessels  of 
Reaumur’s  porcelain ;  and  by  this  means,  not  only  would  the 
time  expended  be  materially  abridged,  and  fuel  economized, 
but  the  manufacturer  would  be  relieved  from  one  of  the  great¬ 
est  practical  difficulties  which  has  been  found  to  attend  the 
conversion,  and  which  arises  from  the  tenacity  wherewith  the 
sand  usually  employed  is  found  to  adhere  to  the  glass. 

This  evil  is  frequently  experienced  to  so  great  a.  degree,  that 
the  force  required  for  their  separation  endangers  the  breaking 
of  the  vessel.  Moulds  of  every  requisite  form  might  be  made 
without  difficulty,  of  substances  sufficiently  refractory  to  remain 
uninfluenced  by  the  temperature  employed  for  the  conversion, 
and  which  would  deliver  the  glass  freely  upon  its  completion. 

M.  Guyton-Morveau  read,  in  1810,  before  the  French  Na¬ 
tional  Institute,  a  paper  containing  observations  with  a  view  to 
explain  some  phenomena  that  occur  in  the  fabrication  of  glass.* 
In  the  course  of  his  remarks,  this  celebrated  chemist  drew  the 
attention  of  his  auditors  to  several  specimens  of  devitrified  glass 
collected  by  him,  which  had  been  rendered  opaque  and  fibrous 
by  the  long-continued  action  of  heat  in  a  porcelain  furnace. 
Some  of  these  pieces  were  converted,  without  having  been  sur¬ 
rounded  by  sand  or  gypsum,  or  any  other  cementing  substance, 
and  yet  exhibited  the  completest  change  throughout  their  sub¬ 
stance. 

One  of  his  specimens,  composed  of  bottle  glass,  had  been  ex¬ 
posed,  during  three  entire  days,  to  the  heat  of  50  degrees  of 
Wedgwood’s  pyrometer,  and  had  acquired  interiorly  a  rosy  tint, 
its  fracture  exhibiting  fibrous  lines,  arranged  in  the  form  of 
stars,  and  converging  towards  the  centre :  this  glass  was  suffi¬ 
ciently  hard  to  scratch  rock  crystal.  Another  specimen  of  flint 
glass,  which  had  been  exposed  during  the  same  time,  in  the 
same  furnace,  exhibited  only  the  commencement  of  crystalliza¬ 
tion  at  its  surface;  the  interior  retaining,  unaltered,  its  original 
vitreous  quality. 

M.  Guyton-Morveau  likewise  exhibited  some  artificial  intag¬ 
lios,  made  of  bottle  glass,  which  had  been  first  softened  and 
moulded  in  a  cupelling-furnace,  on  an  impression  taken  with 
rotten-stone,  and  subsequently  devitrified  in  the  heat  of  a  por¬ 
celain  furnace.  These  specimens  were  sufficiently  hard  to 
scratch  rock-crystal ;  a  quality  which  points  out  the  fitness  of 
such  productions  to  be  used  as  dies  for  the  preparation  of  in¬ 
taglios  and  cameos,  the  impression  which  they  receive  and  im¬ 
part  being  exceedingly  chaste  and  perfect.  The  same  quality 
suggests  the  advantage  that  would  probably  be  found  in  the  em- 


*  Ann.  (Ip  Chim.  voj.  lxxiii.  p.  113. 


CHAP.  XVI.  REAUMUR’S  PORCELAIN.  249 

ployment  of  Reaumur’s  porcelain  in  the  composition  of  mock 
onyxes ;  but,  for  this  purpose,  the  ground  and  figures  must  be 
formed  of  separate  layers  of  different-colored  glass,  which  must 
be  brought  together  by  means  of  some  fluxing  material,  and 
afterwards  devitrified,  in  order  to  give  them  the  requisite  opa¬ 
city,  and,  in  some  degree,  also,  that  hardness  which  is  the  dis¬ 
tinguishing  characteristic  of  gems. 

One  specimen,  also  brought  forward  on  the  same  occasion  by 
M.  Guyton-Morveau,  was  a  segment  of  a  globe,  composed  of 
bottle-glass,  which  had  been  cut  in  the  form  of  a  watch-glass, 
to  be  used  as  a  capsule,  and  afterwards  devitrified.  This  piece 
might  be  suddenly  heated  red-hot,  and  immediately  thrown  into 
cold  water,  without  experiencing  injury.  It  might  also  be  kept 
in  heated  sulphuric  acid,  without  exhibiting  the  least  corrosion 
or  alteration  of  weight ;  two  qualities  calculated  to  render  its 
employment  eminently  advantageous  for  the  purposes  of  chem¬ 
ical  analysis. 

The  result  of  different  experiments  made  to  devitrify  stained 
glass  taken  from  church  windows,  was  likewise  shown,  on  the 
same  occasion,  by  M.  Guyton-Morveau.  Of  various  pieces  thus 
treated,  some  were  colored  red  by  the  precipitate  of  Cassius, 
and  others  blue  by  oxide  of  cobalt.  One  of  the  red  specimens 
contained  lead  in  its  composition ;  this,  on  losing  its  transparent 
quality,  had  become  of  a  spongy  consistency,  and  appeared  full 
of  blebs ;  in  the  other  piece,  which  was  hard  crown-glass,  the 
devitrification  was  seen  to  have  pursued  its  usual  and  regular 
course,  interiorly  from  the  two  surfaces :  it  had  acquired  a  pur¬ 
ple  tinge,  and  was  so  little  hardened  that  it  might  be  scratched 
by  rock-crystal.  The  piece  which  had  been  stained  by  oxide 
of  cobalt  differed  from  the  last  in  more  than  one  particular.  Its 
hardness  was  so  great,  that  scarcely  could  any  perceptible  mark 
be  made  upon  it  by  adamantine  spar ;  its  blue  color,  which  had 
the  appearance  of  being  somewhat  weakened  internally,  was  at 
the  same  time  more  intense  at  the  surface,  a  variance  which 
might,  indeed,  be  more  apparent  than  real,  and  which  probably 
resulted  from  the  greater  opaqueness  it  had  acquired  at  that 
part;  as  although  the  glass  had  lost  all  transparency,  the  devi¬ 
trification  was  by  no  means  perfect,  having  proceeded  but  a 
short  distance  below  the  surface. 

Glass  has  been  converted  into  Reaumur’s  porcelain  during 
volcanic  eruptions,  by  being  enveloped  in  burning  lava.  Some 
specimens  of  this  kind  were  obtained  after  the  destruction  of 
Torre  del  Greco,  in  1794 ;  but  it  is  somewhat  remarkable,  that 
this  devitrifying  effect  has  been  by  no  means  uniformly  exhibit¬ 
ed  under  the  same  circumstances,  since  pieces  of  glass  have 
been  found,  which,  although  completely  embedded  between  two 


250 


GLASS  MANUFACTURE. 


CHAP.  XVI. 


opaque  volcanic  crusts,  yet  retain  their  transparency  and  vitre¬ 
ous  qualities.  The  examination  of  these  particular  specimens 
does  not  appear  to  have  been  carried  sufficiently  far  to  deter¬ 
mine  the  fact ;  but  it  is  by  no  means  unlikely  that  the  varying 
effect  here  noticed  may  have  been  owing  to  some  difference  in 
their  original  composition. 

The  greater  the  number  of  suitable  ingredients  that  are  em¬ 
ployed  in  the  composition  of  glass,  the  more  easily  and  promptly 
does  it  become  devitrified.  This  circumstance  will  sufficiently 
account  for  the  fact  of  bottle-glass  being  the  most  suitable  of 
any  for  conversion  into  Reaumur’s  porcelain.  Having  been 
compounded  without  much  attention  to  the  purity  of  its  ingre¬ 
dients,  this  substance  contains  a  great  variety  of  earthy  salts  in 
minute  quantities;  while  plate  glass,  which  is  a  much  more 
simple  body,  and  in  the  manufacture  of  which  the  purified  in¬ 
gredients  are  brought  together  in  the  precise  proportions  that 
are  required  exactly  to  saturate  each  other,  can  be  devitrified 
only  partially,  and  with  great  difficulty. 

On  the  other  hand,  in  the  same  manner  as  a  solution  com¬ 
pounded  of  a  great  variety  of  saline  bodies  forms  its  crystalline 
deposits  in  a  confused  manner,  so  is  it  also  observed  that  the 
fewer  the  number  of  ingredients  which  are  contained  in  devit¬ 
rified  glass,  the  greater  is  the  degree  of  regularity  whereby  its 
fibrous  arrangement  is  attended  ;  and  for  this  reason  plate  glass, 
where  the  difficulty  attending  its  devitrification  has  been  over¬ 
come,  furnishes,  if  not  the  most  complete,  yet  certainly  the 
most  regular  and  beautiful  specimens  of  Reaumur’s  porcelain. 

It  has  been  observed  that  glass,  when  devitrified,  becomes  a 
much  more  perfect  conductor  of  heat  and  electricity  than  it  was 
before  it  had  changed  its  vitreous  form.  In  fact,  several  pieces 
of  glass,  when  converted  into  Reaumur’s  porcelain,  could  not 
be  made  to  exhibit  any  sign  of  electricity  by  friction.  This 
circumstance  is  rendered  yet  more  remarkable  by  the  fact,  that 
glass  which,  having  been  once  devitrified,  has  been  made  to 
resume  its  vitreous  form  by  fusion,  although  it  is  thereby  re¬ 
invested  with  its  original  density,  fracture,  and  other  charac¬ 
teristics,  yet  shows  no  greater  disposition  to  become  electric 
than  it  exhibited  during  its  state  of  devitrification. 


INDEX. 


A. 

AIKIN,  Messrs.,  their  experiments 
on  the  composition  of  glass,  133. 
Allint,  M.  his  experiments  on  the, 
manufacture  of  bottle  glass,  152. 
Alumina,  34. 

Astbury  discovers  theElere’  method 
of  glazing  porcelain,  25. 

Aristotle,  his  problems  respecting 
glass,  106. 

Attilianus,  20. 

B. 

Bamboo  of  Wedgwood,  28. 

Basaltes  of  Wedgwood,  28. 

Beads,  manufacture  of,  182.  Imita¬ 
tion  of  pearl,  184.  Manner  of  their 
invention  and  formation,  ib. 

Bede,  the  venerable,  his  account 
glass  in  England,  112. 

B lan court,  his  account  of  the  dis¬ 
covery  of  casting  plate-glass,  114. 
Blowpipe,  description  of,  177. 
Blunging,  process  of,  41. 

Bricks,  antiquity  of  the  manufacture 
of,  18.  Roman  manufacture  of,  ib. 
Brindley,  his  improved  flint-mill,  42. 
Brongniart,  M.,  his  receipt  for  the 
manufacture  of  tender  porcelain,  46. 
Buckingham,  second  duke  of,  his  en¬ 
couragement  of  the  manufacture  of 
British  glass,  115. 

C. 

Carlsbad,  mineral  springs  of,  36. 
Caylus,  Count,  his  account  of  ancient 
colored  glass,  219. 

Chaptal,  M.,  his  direction  for  making 
glass  from  calcined  bones,  175.  His 
process  for  forming  white  enamel, 63. 
Clay,  analysis  and  description  of,  84. 
Wedgwood’s  experiments  on,  ib. 
Further  analysis  of,  35.  Species  of, 
used  in  the  potteries  of  Staffordshire, 
37.  Blue  clay  the  best,  38.  China 
clay,  ib.  Dilution  of,  in  potteries,  40. 
Cobalt,  oxide  of,  used  as  coloring 
matter  in  the  manufacture  of  por¬ 
celain,  21. 

Colbert,  Monsieur,  patronizes  the 
manufacture  of  glass  in  France,  113. 
Cookworthy,  his  manufacture  of  por¬ 
celain,  29. 

Crazing,  meaning  of  the  term,  37. 

D. 

De  Botticher,  baron,  discovers  the 
composition  of  true  porcelain,  22. 
D’Entrecolles,  Francis  Xavier,  mis¬ 
sionary  in  China,  22. 

De Montamy, M.,  his  recipe  for  com¬ 
posing  a  pure  white  color,  77. 

De  Montigny,  M.,  furnace  of,  57. 

De  Palissy,  Bernard,  his  improve¬ 
ments  in  enamelling,  64.  His  dis¬ 
tresses  and  perseverance,  65. 
Dial-plates  of  watches  and  clocks, 
how  formed,  185.  Lettering  and 
figuring,  188. 

Durcos,  M.,  his  experiments  on  the 
manufacture  of  bottle  glass,  152. 

E. 

Elers,  the  two  brothers,  their  manu¬ 
facture  of  porcelain,  25. 

Enamel,  coloring,  antiquity  ofi  69. 

F. 

Faraday,  Mr.,  his  experiments  re¬ 
specting  the  manufacture  of  heavy 
glass,  134. 

Felspar,  Cornish,  its  fusibility,  39. 
Flint,  analysis  of,  36.  Process  for 
the  preparation  of*  for  the  manufac¬ 
ture  of  porcelain,  42. 

Fontanieu,  M.,  his  direction  for  the 
composition  of  artificial  gems,  171. 
His  recipe  for  the  color  of  the  ame¬ 
thyst,  215;  of  the  emerald, 'HO.  His 
receipt  for  the  lustre  of  the  semi¬ 
transparent  opal,  216. 

Frauenhofer,  rises  from  obscurity  by! 
his  talents;  his  «  icntific 


ments,  201.  Produces  specimens  of 
perfect  glass ;  dies  at  an  early  age,  ib. 

O. 

Gehlen,  M.,  his  recipe  for  crown 
glass,  145. 

Gems,  composition  of,  35. 

Gems,  artificial;  great  interest  for¬ 
merly  attached  to  the  subject,  171. 
Modes  of  preparation,  ib.  Rock 
crystal  formerly  employed,  172. 
Diamond  paste,  173.  Various  pastes 
for  imitating  different  gems,  174. 
Geobert,  M.,  his  analysis  of  the  por¬ 
celain  earth  of  Baudissero,  39. 
Gerhard,  his  experiments  on  granite, 
38. 

of  Glass,  nature  of,  105.  Its  various 
properties,  ib.  Its  utility,  106. 
Value  of  it  anciently,  107.  Origin 
of  the  word  ;  Aristotle’s  problems 
respecting  it,  108.  A  Pheniciau  in¬ 
vention,  ib.  Manufactories  of  Alex¬ 
andria,  109.  Malleable  glass,  ib. 
Discussion  on  the  malleability  of, 
110.  Tax  imposed  on  by  Alexander 
Severus;  Portland  vase;  employed 
in  forming  windows,  111.  Manufac¬ 
tured  in  Britain  prior  to  the  Ro¬ 
man  invasion,  ib.  Extract  from 
the  ‘‘Northumberland  Household 
Book,”  112.  Privileges  granted  to 
manufacturers  in  France,  ib.  Plate 
glass  casting,  113.  Establishment 
at  8t.  Gobain,  114.  Flint  glass, 
manufacture  of, commenced  in  Eng¬ 
land,  115.  Plate  glass  manufactured 
in  England,  ib.  Chinese  unacquaint¬ 
ed  with  glass-making,  116.  Import¬ 
ance  of  the  manufacture  in  England, 
ib.  Madeasourceof  revenue,117.  In¬ 
gredients  employed  in  the  manufac¬ 
ture  of,  119,  Silex  and  alkali  essen¬ 
tial  to  the  formation  of  glass;  pot¬ 
ash  and  pearl-ash  used  also,  120. 
Barilla;  kelp,  ib.  Borax  and  chalk 
used  in  the  manufacture  of,  124. 
Construction  of  a  furnace  for,  125. 
Three  kinds  of  furnaces  used  in  the 
manufacture  of,  126.  The  calcar; 
the  fritting  process,  ib.  Double  fur¬ 
nace;  proportionate  dimensions  of 
furnace  and  pots,  128.  Comparative 
consumption  of  fuel  in  wood  and 
coal  furnaces ;  annealing  oven,  129. 
Glass  pots  ,■  their  formation  and  sea¬ 
soning,  130.  Manufacture  of  flint 
glass,  131.  Importance  of  its  quality 
for  optical  purposes;  experiments 
for  its  improvement,  132.  Process 
of  melting,  134.  Glass  gall,  135.  Im¬ 
plements  used  in  the  manufacture 
of;  rod,  186.  Marvar,  137.  Paraison  ; 
blowing,  ib.  Re-heating;  elongat¬ 
ing,  138.  Pontil,  ib.  Procello; 
fashioning,  139.  Detaching,  ib.  Re¬ 
moval  to  annealing  oven;  mould¬ 
ing;  annealing  indispensable,  140. 
Bologna  phials;  Rupert’s  drops,  ib. 
Crown  glass,  description  of,  143.  Its 
composition  in  France ;  in  England ; 
fritting,  144.  Recipes  for  crown 
glass,  145.  Blowing;  re-heating; 
flattening,  146.  Twirling  ;  expand¬ 
ing;  opening,  147.  Bull’s  eye,  ib. 
Annealing ;  nice  regulation  of  tem¬ 
per  aturein  this  process ;  qualities  of 
crown  glass,  148.  Broad  glass  ;  in¬ 
ferior  to  crown  glass;  its  composi- 
tion  ;  preparation,  ib.  Working; 
bursting  ;  annealing,  149.  Bottle 
glass;  manufacture  of,  checked  by 
an  increase  of  duty,  ib.  Composi¬ 
tion  ;  restrictions  as  to  materials; 
theiy  bad  tendency.  160.  Superiori  ty 
of,  for  certain  purposes,  ib.  Mate¬ 
rials  employed;  in  France;  at  New¬ 
castle,  161.  Fashioning;  moulding. 
Experiments  of  Count  Chaptal, 
Volcanu  gra¬ 


nite,  164.  Plate  glass:  blown  plates 
limited  in  size,  ib.  Cast  plate  works 
at  Ravenhead ;  difficulties  of  tha 
process;  materials,  165.  Furnaces 
and  crucibles  at  St.  Gobain,  167. 
Method  for  regulating  the  supply  of 
fue'  at  St.  Gobain,  158.  Casting 
tables,  ib.  Arrangement  of  the  fuun- 
dery  at  Ravenhead,  159.  Process  of 
easting  plates,  ib.  Squaring;  grind¬ 
ing,  161.  Economical  improvement ; 
smoothing  ;  emery  powder,  162. 
Comparative  value  of  large  and 
small  plates,  163.  Polishing,  164. 
Silvering,  165.  Preparation  of  amal¬ 
gam,  ib.  Mode  of  its  applicat  ion,  166. 
Process  of  blowing,  167.  Punching, 
168.  Partial  cutting,  ib.  Transfer 
to  pontil;  completion  of  cutting,  169. 
Opening,  ib.  Sizes  of  plates;  effects 
of  the  Bun's  rays  on,  170.  Phos¬ 
phoric  glass,  pieparation  of  bones 
for  ;  their  vitrification  ;  process 
known  to  Becher;  concealed  by 
him,  175.  Curious  suggestion  as  to 
its  employment:  this  glass  highly 
electric  when  newly  made,  ib.  Va¬ 
rious  small  manufactures  of  glass, 
176.  Thermometer,  177.  Blow-pipe, 
ib.  Method  of  working,  178.  oeal- 
ing  tubes,  ib.  Bending  and  joining 
tubes,  179.  Forming  bulbs  at  the 
ends  of  tubes,  180.  Watch  glasses, 
ib.  Lunette  glasses;  glass  beads,  162. 
Striped  tubes  ;  mode  of  forming 
beads,  183.  Mock  pearl  beads,  164. 
Principal  defects  observable  in  glass, 
192.  Striae  ;  threads,  193.  Tears, 
ib.  Knots:  bubbles;  whence  they 
proceed,  194.  Bubbles  not  very  det¬ 
rimental,  ib.  Specific  gravity  of, 
202.  Augmented  by  lime,  204.  Mix¬ 
ed  glasses,  205.  Their  spc<  ific 
weight,  206.  Specific  gravity  in¬ 
fluenced  by  temperature,  207.  The 
art  of  coloring  it,  and  the  antiquity 
of  the  art  ;  specimens  of  Roman 
mosaic,  208.  Analysis  of  these  by 
Klaproth,  209.  Metallic  oxides,  2.U. 
Gold-purple;  its  great  coloring  pow¬ 
er,  ib.  Kunckel’s  proficiency  in  the 
art  of  staining  glass,  2ll.  Directs 
the  ope rationsof  glass-houses  at  Pots¬ 
dam,  212.  Yellow  color  from  silver; 
from  lead,  ib.  From  tartar;  from 
beech-wood  charcoal,  213.  From 
oxide  of  iron,  green,  black  glass,  ib. 
Red,  214.  Blue  :  directions  found 
in  old  authors,  215.  Imitation  of 
the  garnet ;  of  the  amethyst,  ib.  Of 
the  emerald,  216.  Of  sapphires,  ib. 
Opaque  glass;  black,  217.  Whits 
opaque  glass,  ib.  Opal, 218.  Ancient 
pictures  formed  of  colored  glass,  ib. 
How  executed,  219.  Accidental  col¬ 
oring  of  plate  glass  at  St.  Gobain, 
221.  The  art  of  cutting,  engraving, 
and  etching  on ;  origin  of  the  art  of 
cutting,  235.  Implements  used  in 
cutting, ib.  Frosting,  238.  Patterns 
produced  by  moulding,  ib.  Engrav¬ 
ing  on  glass,  239.  Etching, 240.  In¬ 
crustations;  origin  of  the  art,  242. 
The  devitrification  of,  243.  Devit- 
rified  glass;  uses  to  which  it  may 
be  applied,  244.  Common  bottle 
glass  best  suited  to  it ;  method  of 
effecting  the  change,  ib.  Experi¬ 
ments  of  Dr.  Lewis,  245.  Revitri¬ 
fication  of,  216.  Experiments  of 
Sir  James  Ilall,  247.  Glass  con¬ 
verted  into  Reaumur’s  porcelain, 
by  burning  lava,  219. 

Glazes  for  porcelain  generally  *  analy¬ 
sis  of  that  used  by  the  French,  64. 

Green,  Mr.,  proprietor  of  Stangate 
glass-house;  his  specimens  of  good 
heavv-glass,  196. 

Guinand,  M.,  his  humble  origin; 
energy  of  character,  190.  Ex  ami  nut 


ib. 

ai  quite*'  162.  Klingt-tein,  163. 


INDEX 


252 

telescopes,  and  constructs  others; 
unable  to  procure  glass  of  good  qual¬ 
ity,  190.  Is  incited  to  examine  into 
the  causes  of  inferiority;  his  extra¬ 
ordinary  perseverance  amidst  acci¬ 
dents  and  difficulties,  197.  His  ulti¬ 
mate  success,  198.  Accident  lead¬ 
ing  to  further  improvement,  199. 
Prosecutes  his  art  in  Bavaria;  re¬ 
turns  home,  and  further  pursues  his 
favorite  object,  200.  Dies,  201. 

H. 

Hall,  Sir  James,  he  experiments  on 
compression  in  modifying  the  action 
of  heat,  217. 

Hanway,  Jonas,  his  account  of  Chi¬ 
nese  palace  at  Dresden,  2*4. 
Herculaneum,  utensils  of  glass  found 
in  the  ruins  of,  109. 

J. 

Jao  teheou,  precious  jewels  of,  97. 
Jaquin,  M.,  his  invention  of  mock- 
pearl,  184. 

Jasper-ware  of  Wedgwood,  28. 

K. 

Kao-lin,  analysis  of,  93. 

Keyaler,  his  description  of  a  mode  of 
composing  pictures  in  colored  glass, 
220. 

Kia-tsing,  99. 

King-te-ching,  porcelain  manufacto¬ 
ries  of,  94. 

Klaproth,  his  investigations  respect¬ 
ing  the  capability  of  dissolving  silex 
in  water,  36.  His  analysis  of  the 
specimens  of  Roman  mosaic,  209. 
His  analysis  of  ancient  blue  glass, 
ib.  His  account  of  ancient  mosaics, 
220. 

Ku-tong,  101. 

L. 

Lathe,  potter’s,  description  of,  48. 
Lenses,  formation  of ;  preparation  of 
the  necessary  tools,  189.  Choice  of 
glass  for,  190.  Grinding  and  polish¬ 
ing,  ib. 

Loysel,  M.,his  direction  for  the  con¬ 
struction  of  a  fhrnace  in  the  manu¬ 
facture  of  glass,  126.  Recommends 
the  use  of  minium  in  the  manufac¬ 
ture  of  flint  glass,  132.  His  recipe 
for  the  formation  of  crown  glass, 
144.  His  account  of  the  composi¬ 
tion  of  bottle  glass  in  France,  151. 
His  account  of  the  composition  of 
plate  glass,  at  St.  Gobain,  156.  His 
recipe  for  the  composition  of  arti¬ 
ficial  gems,  173.  His  experiments 
on  the  specific  gravity  of  glass,  202. 
Lunette-glasses,  manufacture  of,  182. 
Lustre-ware,  gold  and  silver,  bO. 

M. 

Macquer,  his  remarks  on  Reaumur’s 
experiments  concerning  porcelain, 
23.  Furnace  of,  67. 

Manganese,  black  oxide  of,  used  for 
clearing  glass,  122. 

Mansell,  Sir  Robert,  obtains  a  mo¬ 
nopoly  for  manufacturing  glass  in 
England,  116. 

Modeller, qualifications  requisite  for, 

Morveau,  Monsieur  Guyton,  his  ex¬ 
periments  on  the  specific  gravity  of 
melted  glass,  121.  His  observations 
on  the  devitrification  of  glass,  248. 
Moulds,  method  of  making  them,  62. 

N. 

Neri,  his  recipe  for  imitating  the 
garnet,  216.  His  recipe  for  white 
opaque  glass,  218. 

Neumann,  first  observes  the  devitri¬ 
fication  of  glass,  243. 

Nungarrow,  factory,  superiority  of 
its  porcelain,  56. 


P. 

Pipes,  tobacco,  manufacture  of  prose¬ 
cuted  to  a  great  extent;  description 
of  material,  86.  Boring,  moulding, 
polishing,  baking,  87.  Description 
of  the  kiln  of  crucibles,  88.  Manu¬ 
facture  of,  prosecuted  to  a  great  ex¬ 
tent  in  Holland.  89.  Originally  con¬ 
veyed  thither  from  England,  ib. 

Polo,  Marco,  his  mention  of  the  por¬ 
celain  manufacture  of  China,  96. 

Porcelain,  17.  Antiquity  of,  18. 
Made  in  Japan  at  nn  early  period, 
20.  Oriental  porcelain  common  in 
Europe  in  the  first  century,  ib.  An¬ 
tiquity  of  the  manufacture  of  in 
Egypt,  21.  Probable  origin  of  the 
word,  ib.  Manufactured  in  Saxony 
by  baron  de  Botticher,  22.  Reau¬ 
mur’s  experiments  respecting,  23. 
Hanway’s  account  of  that  manufac¬ 
tured  at  Dresden,  24.  Antiquity  of 
manufacture  in  Staffordshire,  25. 
Manufactured  by  the  two  brothers 
named  Elers,  ib.  Manufacture  of, 
important  to  England,  30.  Manu- 
facturedat  Lambeth ;  Derby;  Shrop¬ 
shire;  Yorkshire;  at  the  Rocking¬ 
ham  works,  31.  A  tax  imposed 
upon  stone  battles,  33.  Ingredients 
used  in  the  manufacture  of  pottery, 
34.  The  quality  of  clay  used  in  the 
manufacture  of,  ib.  Steatite  or  soap¬ 
stone  used  in  the  manufacture  of, 
39.  Spuma  maris  used  in  its  manu¬ 
facture,  40.  Quality  of  water  used, 
ib.  The  process  of  blunging,  41. 
Process  for  preparing  the  flint,  42. 
Utility  and  description  of  Brindley’s 
mill  in  the  preparation  of, ib.  Slip; 
slip-kiln,  43.  Slip-house,  44.  The 
process  of  slapping  in  the  manufac¬ 
ture  of,  45.  Method  of  manufactur¬ 
ing  in  France  not  kept  so  secret  as 
that  in  England,  ib.  Calcined  bones 
used  in  the  manufacture  of,  46.  The 
earth  used  in  Berlin,  47.  The  for¬ 
mation  of  utensils  in  the  manufac¬ 
ture  of;  the  process  of  throwing, 
48.  Milled  edges;  the  handler,  61. 
Method  of  ornamenting  porcelain 
described,  ib.  Method  of  making 
moulds,  52.  Boiled  plaster  used  in 
making  moulds,  ib.  Increasing  skill 
of  artists,  63.  Mould-maker;  meth¬ 
od  of  his  working,  64.  Method  of 
casting,  ib.  Beggars  of  imperfect 
materials  in  England;  Nungarrow 
factory,  67.  Furnace  of  MM.  de 
Montigny  and  Macquer,  67.  The 
biscuit-oven  of  Worcester:  Chinese 
method  of  firing,  60.  Duration  of 
the  baking  process ;  oven-man  ;  trial 
pieces,  61.  Composition  of  raw 
glazes  ;  bad  effects  of  them,  62. 
Glazes  generally,  63.  Inferior  glazes ; 
low-priced  wares,  66.  Regulation  of 
temperature,  ib.  Qualities  of  good 
porcelain;  stone-ware,  67.  Painted 
ware  of  Worcester  ;  of  Stafford¬ 
shire;  of  Derby;  of  Yorkshire,  69. 
Metallic  oxides,  70.  Addition  of 
fluxing  bodies  necessary,  ib.  Ve¬ 
hicle  used  with  the  colors,  73.  Pur¬ 
ple  and  violet,  74.  Red,  75.  Yel¬ 
low,  ib.  Blue,  76.  Green;  brown; 
black,  77.  White,  78.  Compound 
colors,  79.  Giiding  ;  lustre-ware  ; 
preparation  of  colors,  80.  Enamel¬ 
ling  kilns,  ib.  Trial  pieces,  81.  Gild¬ 
ing  and  burnishing,  ib.  Analysis  of 
the  fluxes  and  recipes  for  colors,  83. 
Method  of  transferring  copperplate 
designs  to  porcelain,  84.  French 
method,  85.  Manufacture  of  in  Chi¬ 
na,  90.  Supposed  superiority  of  old 
China-ware,  ib.  Materials  employ¬ 
ed  ;  kao-lin;  pe-tun-tse;  their  pre¬ 
paration,  91.  Oils  or  varnjphes ; 
their  composition,  92.  Hao-che 
superior  to  kao-lin,  93.  Analysis  of 
kao-lin,  ib.  Extent  of  factories  at 
King-te-ehing  ;  great  number  of 


workmen,  94.  Preparation  of  ma¬ 
terials,  ib.  Method  of  fashioning 
utensils  ;  moulds,  ib.  Division  of 
labor,  95.  Deficiency  of  the  Chinese 
in  the  art  of  design,  96.  Blue  first 
the  only  color  used,  97.  Chinese 
ignorant  of  chemical  science,  98. 
Umiam;  tsou-tchi,  99.  Kia-tsing 
method  of  forming  it,  ib.  Chinese 
furnaces,  100.  Passion  for  old  por¬ 
celain,  101.  Ku-tong,  ib.  Mock 
antiques;  reasons  for  the  costliness 
of  China-ware  in  Europe,  ib.  Por¬ 
celain  tower,  ib.  Tse-ki ;  attempt 
of  the  emperor  to  transfer  the  ma¬ 
nufacture  to  Pekin,  102. 

Pottery,  antiquity  of,  18.  Made  in 
England  before  the  invasion  of  the 
Romans,  19.  Antiquity  of  in  China, 
20. 

Pyrometer  of  Wedgwood,  35. 

R. 

Reaumur,  experiments  of,  concern¬ 
ing  the  manufacture  of  china,  23. 
Hi9  experiments  upon  the  devitri¬ 
fication  of  glass;  his  porcelain, 243. 
Rockingham,  -the,  porcelain  manu¬ 
factory,  31. 

Rose,  Mr.  John,  his  glaze  for  hard 
porcelain,  63. 

Rykum,  boiling  fountain  at,  36. 

8. 

Schwanhard,  Henry,  his  method  of 
etching  on  glass,  240. 

Seggars,  proper  materials  for  the  con¬ 
struction  of  them  wanting  in  Eng¬ 
land,  65.  Use  of,  66. 

Severus,  Alexander,  his  tax  on  glass, 

111. 

Silica,  34.  Analysis  of,  36. 

Slapping,  the  process  of,  45.  Per¬ 
formed  by  steam  power,  46. 

Slip,  the  mixture  used  in  porcelain 
manufacture,  43. 

Spuma  maris,  its  employment  in 
porcelain  works  In  Spain,  40. 

Steat  ite,  or  soapstone,  Cornish,  analy¬ 
sis  of,  39. 

St.  Gobaiu,  glass  manufactory  at,  114. 

Its  early  failure  and  revival,  ib. 
Stone-ware,  its  composition,  67.  Best 
description  of  it  made  at  Lambeth, 
ib. 

T. 

Table-ware  of  Wedgwood,  27. 
Terra-cotta  of  Wedgwood,  28. 
Thevart,  his  invention  of  plate  glass, 
113. 

Thermometer  tubes,  176.  Mode  ot 
giving  them  an  elliptical  bore,  177. 
Throwing,  the  process  of,  48. 
Tower-porcelain,  at  Nan-king,  101. 
Tsou-tchi,  99. 

Turning-lathe  of  the  potter,  49. 

V. 

Vasa,  Murrhina,  formed  out  of  a 
transparent  stone,  20. 

Vase,  Portland  or  Barberini,  53. 
Farther  account  of,  111* 

W. 

Watch -glasses,  manufacture  of,  180. 
Lunette-glasses,  182. 

Webber  models  of  Portland  or  Bar¬ 
berini  vase,  63. 

Wedgwood,  Josiah,  his  improvement 
in  the  manufacture  of  porcelain, 
26.  His  table-ware,  27.  Queen’s- 
ware  ;  terra-cotta;  basaltes;  white 
porcelain  biscuit;  bamboo;  jasper, 
28.  His  porcelaiu  biscuit  used  by 
chemists,  ib.  His  evidence  before 
a  committee  of  the  privy  counril,  29. 
His  pvrometer,  36.  His  encour¬ 
agement  to  artists,  53.  His  great 
services  in  the  painting  of  porce¬ 
lain,  69. 

White  porcelain  biscuit  of  Wedg¬ 
wood,  26. 


THE  END 


4 


[4 

*yV'-A 


TTY  CENTER 


IBRARY 


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